Dept of Physics

DEPT OF PHYSICS

Researcher : Bai Y

List of Research Outputs

Bai Y., Li S.S., Zheng H.Z. and Wang Z.D., Detecting a set of entanglement measures in an unknown tripartite quantum state by local operations and classical communication, Physical Review A. New York, The American Physical Society, 2006, 74: 022305:1-8.

Researcher : Beling CD

Project Title:	Centre for optical and positron characterization of defects
Investigator(s):	Beling CD, Fung SHY, Ling FCC
Department:	Physics
Source(s) of Funding:	Central Allocation Vote - Major Equipment Project
Start Date:	03/2001

Abstract:

To provide the University of Hong Kong with a well-equipped center for studying point defects in semiconductor and other industrially related materials - a center that's expertise and equipment would also be made available to other universities in Hong Kong according to need.

Project Title:	Developing VE-PALS (variable energy positron annihilation lifetime spectroscopy)
Investigator(s):	Beling CD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	10/2002

Abstract:

To set up a means of taking PALS spectra on solid-state samples using the HKU magnetically guided positron beam.

Project Title:	Developing Variable Energy Positron Annihilation Lifetime Spectroscopy
Investigator(s):	Beling CD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004

Abstract:

To make some positive step towards achieving a successful Positron Field Assisted Moderator (PFAM) by carrying out a series of positron annihilation studies on clean intimate metal-semiconductor junctions; to conduct PFAM investigations on the following semiconductor substrates: GaAs, GaP, GaN and SiC possibly using semi-insulating forms or material; to use the most advanced diagnostic positron spectroscopy techniques, including Coincidence Doppler Broadening Spectroscopy (CDBS) to study any adverse positron trapping at the metal-semiconductor interface.

Project Title:	Positron beam studies of porous silicon
Investigator(s):	Beling CD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	04/2007

Abstract:

Introduction Porous silicon (P-Si) is a material of significant technological interest owing to its luminescence in the visible band (the S-band) [1]. This luminescence cannot only be efficiently produced by laser and electrical excitation, but in addition but can to a significant degree be tuned according to the material’s pore size and state of oxidation [2]. From the theoretical point of view the P-Si also has interest in that the luminescence seems to arise from quantum confinement in the nano-sized pores that form the skeletal structure [3]. There have been numerous studies of P-Si, but only a few of these have involved positron annihilation [4-7]. The present proposal involves using our positron beam to study porous silicon and the silicon dioxide – P-Si interface. The general aim is to show that positron annihilation is useful in determining not only pore size but also pore interconnectivity. In so doing we hope to be able to apply for future RGC funds for a pulsed Ar ion laser for time resolved positron annihilation studies. Study I – Positron annihilation characteristics in porous silicon. The first study is to grow porous Si with different degrees of porosity (0-80%) and subject them to positron beam analysis. This would involve the standard VEDBARS (Variable Energy Doppler Broadening of Annihilation Radiation) technique which probes the P-Si/Si interface as a function of depth. The S (low momentum) parameter, and W (high momentum) parameter are monitored to give information on the pore size. While there have been some positron studies of P-Si [4-7] only one of these has employed a positron beam. Moreover in this positron beam study it was not the VEDBARS technique being used but the VEPALS technique [7]. In addition, however, we would also measure the F-parameter. This technique works by measuring the ratio of 3 gamma annihilation events to the more common 2 gamma annihilation events. For materials with a larger density of pores (high porosity) more ortho-positronium atoms form that have a higher probability of 3 gamma decay. If this were all that was going on, however, things would not be particularly interesting. It turns out, however, that if pores are interconnected ortho-positronium can move from one pore to another and thus diffuse to the surface where it can emit into vacuum with 100% 3 gamma decay. Thus from F-parameter measurement the interconnectivity of the skeletal P-Si can be quantified [10]. In these studies the SiO2/P-Si interface would be a main feature of study, since positrons are particularly effective at noting differences in interface structure. Study II - Positron annihilation characteristics under different oxidation conditions One feature of S-band emission from P-Si that is poorly understood is the variation of photoluminescence intensity under different oxidation conditions. Incorporation of oxygen into the pores generally shifts the luminescence into the blue, but the reason for this is still uncertain. The positron is sensitive to chemical environment via the few percent of core electrons that undergo annihilation. It is hoped that some relevant information may be obtained on this variation with oxygenation using positron annihilation. The VEDBARS technique is particularly sensitive to the presence of oxygen [8]. Study III - Positron annihilation characteristics under electro-luminescence The feature of the S-band emission that makes P-Si technologically important is the fact that it can be stimulated by an electrical bias applied to a Schottky barrier made from P-Si. The beauty of this type of electroluminescence is its simplicity and high photon yield. Emission, moreover is over the visible spectrum. To construct such a LED, is relatively simple. One just forms an ohmic contact on the rear of the p-Si, and a semi-transparent Au or ITO thin film on the surface of the P-Si. A positive potential being applied to the p-Si drives the Schottky contact into forward bias and light emission over the visible band S-band occurs [11]. I am not aware of any positron annihilation experiment that has been performed on an electrically biased light emitting P-Si structure. It is thus proposed that an experiment be carried out where we apply a bias to a Au/P-Si/pSi device structure while carrying out positron annihilation experiments at the same time. The electro-luminescence would be monitored by a photomultiplier tube attached to the positron beam via an optical fiber positioned close to the sample. Correlations would be sought between the luminescence output and the positron annihilation parameters. This type of experiment is valuable for confirming the most likely theory for the S-band photoluminescence, which is the quantum confinement effect which causes the effective band gap of the Si to increase. The normal luminescence of Si is thereby shifted from the IR into the visible. There are competing defect [12] and amorphous Si [13] theories that cannot be ruled out. If these defect state models have validity then the positron may be a helpful probe since it can trap differently at defects according to their charge states. Biasing would change the charge state of defects. References [1] N. Koshida and H. Koyama, Appl. Phys. Lett. 60 , 347 (1992) [2] T. Wadayama, S. Yamamota, and A. Hatta, Appl. Phys. Lett 65, 1653 (1994) [3] L.T. Canham, Appl. Phys. Lett, 57, 1046 (1990) [4] Y. Itoh, H Mukakami, A. Kinoshita, Appl. Phys. Lett 63 (1993) 2792 [5] S. Dannefaer, C. Wiebe, D. Kerr, J. Porous Materials 7 (2000) 323 [6] C. C. Huang, I.M. Chang, J.H. Fan, Y.F. Chen, Phys.Lett A 237 (1998) 183 [7] R. Suzuki, T Mikado, H. Ohgaki, M. Chiwaki,; Phys. Rev. B 49 (1994) 17484 [8] M. Doyama, Y. Suzuki, S. Ishibashi and T. Abe; P.Phys. Condens Matt (1989) S83 [9] C. Wang, J.M. Perz, F. Gaspari, M.Plumb, , Appl. Phys. Lett 62 (1993) 2676 [10] A. vanVeen, R Escobar, H. Shut, S.W.Eijt. C.V. Falub, Mat. Sci Eng. 102 (2003) 2 [11] A. Loni, A.J. Simons, TCox. P.D. Calcott, L.T Canham Elect. Lett 31 (1995) 1288 [12] G.G. Qin, Y.Q.Jia, Sol. State. Common. 86 (1993) 559 [13] R.Fathauer, T. George, A. Ksendzov, R.P. Vasquez, Appl. Phys. Lett 69, (1992) 995

List of Research Outputs

Cheung C.K., Wang R.X., Beling C.D., Djurisic A. and Fung S.H.Y., Positron beam study of indium tin oxide films on GaN, Journal of Physics: Condensed Matter. Bristol, IOP Publishing Limited, 2007, 19: 086204:1-10.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Hui C.W., Zhang J., Zhou T., Ling F.C.C., Beling C.D., Fung S.H.Y., Brauer G., Anwand W. and Skorupa W., Positron annihilation study of hydrothermal grown n-type zinc oxide, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Nahid F., Beling C.D. and Fung S.H.Y., Temperature dependence study of positronium formation in high density polyethylene by positron annihilation lifetime spectroscopy, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3751-3754.

Tam K.H., Cheung C.K., Leung Y.H., Djurisic A., Ling F.C.C., Beling C.D., Fung S.H.Y., Kwok W.M., Chan W.K., Phillips D.L., Ding L. and Ge W.K., Defects in ZnO nanorods prepared by a hydrothermal method, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 20865-20871.

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Wang R., Xu S.J., Shi S., Beling C.D., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au/GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 143505: 1-3.

Wang R., Xu S.J., Beling C.D. and Cheung C.K., Response to "comment on influence of indium tin oxide thin-film quality on reverse leakage current of indium tin oxide/n-GaN Schottky contacts [Appl. Phys. Lett. 90, 046101 (2007)]", Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 046102-1.

Yang D., Zhang J., Leung J.K.C., Beling C.D. and Liu L.B., Coincidence doppler broadening study in electron-irradiated polyurethane, Nuclear Instruments & Methods in Physics Research (Section B). Amsterdam, Elsevier B.V., 2007, 259: 933-936.

Yu D., Zhang J., Cheng V.K.W., Beling C.D. and Fung S.H.Y., Doppler broadening of annihilation radiation spectroscopy study using Richardson-Lucy, Maximum Entropy and Huber methods, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3997-4000.

Researcher : Bohmer CG

List of Research Outputs

Bohmer C.G. and Harko T.C., Bounds on the basic physical parameters for anisotropic compact general relativistic objects, Classical and Quantum Gravity. United Kingdom, IOP, 2006, 23: 6479-6491.

Researcher : Cai X

List of Research Outputs

Cai X., Djurisic A. and Xie M.H., GaN nanowires: CVD synthesis and properties, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 984-989.

Cai X., Cheung K.Y., Djurisic A. and Xie M.H., Growth of cubic and hexagonal InN nanorods, Materials Letters. Amsterdam, Elsevier B.V., 2007, 61: 1563-1566.

Researcher : Cen L

List of Research Outputs

Cen L., Wang Z.D. and Wang S.J., Scalable quantum computation in decoherence-free subspaces with trapped ions, Physical Review A. New York, The American Physical Society, 2006, 74: 032321:1-4.

Researcher : Chau HF

Project Title:	Cryptanalysis of Certain Quantum Cryptographic Applications
Investigator(s):	Chau HF
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2004

Abstract:

To study the interplay and tradeoff between efficiency, error tolerable rate and resources requirements in various quantum crytographic applications. I begin the study by first focusing on quantum key distribution. The outcome is essential in devising new quantum cryptographic protocols that suit specific applications.

List of Research Outputs

Chau H.F., Quantum string seal is insecure, Physical Review A. New York, The American Physical Society, 2007, 75: 012327:1-7.

Leung C.C. and Chau H.F., Weighted assortative and disassortative networks model, Physica A. Amsterdam, Elsevier B.V., 2007, 378: 591-602.

Researcher : Chen X

List of Research Outputs

Chen X., Ling F.C.C., Djurisic A., Brauer G., Anwand W., Skorupa W. and Reuther H., Influence of hydrogen peroxide treatment on Au/n-ZnO contact, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Gu Q., Ling F.C.C., Cheung C.K., Luo J., Chen X., Djurisic A., Brauer G., Anwand W., Skorupa W., Reuther H. and Ong H.C., Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment, In: S. Ashok, P. Kiesel, J. Chevallier, T. Ogino, Materials Research Society Spring Meeting 2007, 9-13 April 2007, San Francisco, Symposium F: Semiconductor Defect Engineering--Materials, Synthetic Structures, and Devices II. Materials Research Society, 2007, 994: F11-15.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Researcher : Chen Y

Project Title:	Pairing symmetry, competing orders and local physics in electron-doped high temperature superconductors
Investigator(s):	Chen Y, Wang ZD, Zhang FC
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	02/2004
Completion Date:	09/2006

Abstract:

To investigate the superconductivity and other competing orders, more specially, spin density wave; to investigate the existence of two possible types of superconducting order parameters at different pockets of the Fermi surface; to investigate the local electronic structure around impurities or vortex cores, both local density of states and nuclear magnetic resonance relaxation rate will be calculated.

Project Title:	Theoretical Studies of Electronic States in Electron-doped High Temperature Superconductors
Investigator(s):	Chen Y, Wang ZD, Zhang FC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004

Abstract:

The electronic structure of electron-doped cuprates has attracted significant interest both experimentally and theoretically in recent years. Substantial asymmetry exists between the less studied electron-doped and intensively studied hole-doped cuprates. In order to elucidate the mechanism of high temperature superconductivity, it is fundamentally important to clarify the origin of the similarity and the differences between the electron-doped and the hole-doped cuprates.

Project Title:	Mixed States in High Temperature Superconductors: Scenario of Competing Orders
Investigator(s):	Chen Y, Zhang FC, Wang ZD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	04/2005

Abstract:

The electronic structure of mixed states in high temperature superconductors (HTS) has attracted significant interest both experimentally and theoretically for past many years. Many important physical phenomena arise from competing orders, including pseudogap, superconductor-insulator transition, which cannot be explained within a conventional theory. It is well established that the competition between d-wave superconductivity (DSC) and antiferromagnetic (AF) orders plays an essential role in determining the vortex state of HTS. In view of the widely used competing order scenario of the HTS in the mixed state and impurity state, together with the fact that the competing order effect has not been considered in some existing theories relevant to mixed state. In this project, we will focus on the field dependence of the vortex structure, Nernst effect and anomalous Hall effect, which are different from conventional superconductors. We believe the competition between AF and DSC may not only provide a coherent way to understand the vortex structure but also gain new insights on the above-mentioned specific features of the experimental measurements. In terms of the results to be obtained, we attempt to understand profoundly some existing experimental results as well as to suggest new experiments to test our predictions.

Project Title:	Unconventional Superconductivity and Novel Electronic States in Three-dimensional Pyrochlore Lattice Materials
Investigator(s):	Chen Y, Wang ZD, Zhang FC
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	07/2006

Abstract:

The study of novel electronic states in condensed matter plays a vital role in the development of fundamental physics and future electronic devices. The subject of geometrical frustration in strongly correlated systems has attracted much interest recently. The geometric arrangement may frustrate a spin-ordered phase and lead to a highly degenerate disordered quantum spin-liquid state. Lifting this degeneracy makes possible the emergence of exotic quantum ground states, such as unconventional super-conductivity. The aim of this project is to undertake a systematic study of the electronic states of two typical geometrically frustrated systems related to unconventional superconductivity: recently synthesized 3D transition-metal pyrochlores, and a checkerboard lattice as its 2D analogy. Various techniques such as Gutzwiller renormalized mean field, self-consistent RPA and exact diagonalization will be employed to investigate their normal states as well as superconducting states. We believe the interplay between geometrical frustration and unconventional super-conductivity in pyrochlores may not only provide a coherent way to understand profoundly some existing experimental results but also suggest new experiments to test our predictions.

Project Title:	Theoretical investigations of novel electronic states in strongly correlated materials
Investigator(s):	Wang ZD, Zhang FC, Chen Y
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2006

Abstract:

(1) A new family of recently synthesized 3D transition-metal pyrochlores exhibits exotic unconventional superconductivity. Extensive studies are now in progress in order to elucidate the mechanism of superconductivity. To reveal the nature of superconductivity in the limit of strong correlation for geometrically frustrated lattices, we will investigate theoretically the electronic structures in the doped Mott insulator by using t-J model on two typical geometrically frustrated systems, 3D pyrochlores and checkerboard lattice as its 2D analogy. The renormalized mean field theory where the original t-J model is replaced by a renormalized Hamiltonian using a Gutzwiller approximation will be employed. It is our hope that these strongly correlated geometrically frustrated structures may reveal unconventional superconductivity. If they do, this may narrow the search for a new class of high temperature superconductor material. Our preliminary results do show some new features of pairing symmetry of superconducting order parameter and how order parameters depend on doping density. As regards checkerboard lattice, a novel unconventional pairing symmetry shows up. We also find a (d+id)-wave state for 3D pyrochlores structure. Our theoretical studies may be relevant to understand recent experimental measurements of 3D pyrochlore structures. (2) We intend to identify the physical systems with the appropriate microscopic models. Systematic studies using various analytical and numerical techniques will be undertaken. For the undoped system, the Heisenberg model will be investigated by using Schwinger boson mean field theory. For the doped case, we may employ the so-called fluctuation-exchange approximation (self-consistent RPA) to take into account the spin fluctuation effect for Hubbard model on pyrochlores/checkerboard lattice from a weak-coupling approach. Other effects such as the multi-orbital effect, inter-site Coulomb interaction and electron phonon coupling will also be included later. We will perform the calculations of various physical properties, including density of states, specific heat and NMR spin-lattice relaxation rate. We also plan to study other frustrated lattices for possible future experiments. In terms of the results to be obtained, we expect to win a deeper understanding of some existing experimental results and also to suggest new experiments to test our predictions. (3) The investigations of the field dependence of vortex structure and low-temperature Hc2 anomalies in cuprate superconductors have attracted significant interest both experimentally and theoretically for past many years. As the competing order effect has not been considered in some existing theories, we start from the mean field treatment of the well-defined t-U-V model which includes the competition between antiferromagnetic and superconducting orders. For given temperature and external magnetic field, we calculate the order parameter self-consistently by solving the corresponding Bogoliubov-de Gennes equations. Our previous studies suggest that the induction of spin/charge density wave may show up inside and around the vortex core. With the increasing of the external magnetic field, our preliminary calculations show that the geometry of vortex structure can take two different forms: conventional vortex lattice (triangular or square), or vortex stripe phases where all the order parameters including spin density wave, charge density wave and d-wave superconductivity exhibit stripe-like behavior. This novel vortex stripe phases may show up at low temperature and adjacent to Hc2. Phase diagram of temperature dependence of Hc2 will be presented as well. Our results may provide a possible understanding of the low-temperature Hc2 anomalies. We will study other interesting physical quantity such as superfluid density, local density of states, spin-lattice relaxation rate and free energy in the vortex lattice state. (4) Measurements of the Nernst effect, a transverse thermoelectric response, reveal a surprisingly large signal above Tc in the vortex liquid regime in high temperature superconductors. Some theoretical works concerning the superconducting fluctuations and quasiparticle contribution of d-density-wave order have been proposed. As noted by Honerkamp et al, the vortex core creation energy can not be either too large or too small. They suggested the presence of staggered flux vortices. It seems to us that some recent NMR experiments do not support such vortices with staggered flux in the core. We still use t-U-V model which allows the local admixture of antiferromagnetic order in the mixed state. According to our previous results, the presence of antiferromagnetic order inside the vortex core gains energy, the creation energy for such antiferromagnetic vortex core is neither large nor small. We will redo the calculations following Honerkamp et al’s work. Our results might be consistent with the large Nernst signal observed experimentally. Other approaches related to pseudogap phase will be utilized to tackle this problem, combining a renormalized mean field study of the t-J model and phase fluctuations. The latter will be treated by a classical Monte Carlo simulation of an XY model. (5) The anomalous Hall effect (AHE) in mixed state of high temperature superconductors has remained an open question for some years. Recent studies have been made of AHE in ferromagnets and colossal magnetoresistance manganites. Their theories connect the anomalous Hall conductance of the system to the Berry phase acquired by a quasiparticle wave function upon traversing closed paths on the Fermi surface. We propose here to study AHE in high temperature superconductors by calculating the topological properties of the system such as Berry phase and Chern number. The related calculations can be performed in a straightforward manner. Firstly we will obtain the quasiparticle wavefunction by diagonalizing the effective Hamiltonian. Next we will compute the Berry phase and Chern number according to a commonly used definition. Finally we connect the obtained topological properties to the Hall conductance of the system. We will also study the Berry phase and Chern number of this vortex structure with the possible induced antiferromagnetic order inside or around the vortex core. These quantities may establish a direct relationship with AHE. We hope to show the relevance between the presence of AF induction and the change of Berry phase and Chern number. Our preliminary study strongly suggests that this connection is significant.

List of Research Outputs

Chen Y., "Theoretical Understanding of Rotational Symmetry Breaking in Sodium-Doped Cuprate Superconductors", TcSUH Special Seminars, Texas Center for Superconductivity at the University of Houston. 2007.

Chen Y., Rice T.M. and Zhang F.C., Atomic scale rotational symmetry breaking in lightly doped Ca_2-xNa_xCuO₂Cl₂, Physica C. Amsterdam, Elsevier B.V., 2007, 460-462: 234-237.

Chen Y., Rice T.M. and Zhang F.C., Rotational symmetry breaking in the ground state of sodium-doped cuprate superconductors, Physical Review Letters. New York, The American Physical Society, 2006, 97: 237004: 1-4.

Chen Y., Wang Z.D., Li Y.Q. and Zhang F.C., Spin-orbital entanglement and quantum phase transitions in a spin-orbital chain with SU(2) x SU(2) symmetry, Physical Review B. New York, The American Physical Society, 2007, 75: 195113:1-5.

Gan J.Y., Chen Y. and Zhang F.C., Superconducting pairing symmetries in anisotropic triangular quantum antiferromagnets, Physical Review B. New York, The American Physical Society, 2006, 74: 094515:1-6.

Huang H.X., Li Y.Q., Gan J.Y., Chen Y. and Zhang F.C., Unconventional superconducting symmetry in a checkerboard antiferromagnet studied via renormalized mean-field theory, Physical Review B. New York, The American Physical Society, 2007, 75: 184523:1-6.

Shen R., Chen Y., Wang Z.D. and Xing D.Y., Conservation of spin currents in spin-orbit-coupled systems, Physical Review B. New York, The American Physical Society, 2006, 74: 125313:1-5.

Researcher : Cheng KS

Project Title:	Properties of strange stars and their observational appearance
Investigator(s):	Cheng KS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2003

Abstract:

To study the emissivity and transport properties of electronmagnetic waves in semi-degenerate and inhomogeneous electron gas of the strange star atmosphere; the thermal emissivity of hot quark surface in electron-positron pairs; to calculate electron-positron pairs more precisely, hopefully with accuracy of ~10% or even higher; to study electromagnetic waves produced by passing the quarks and also the propagation of electromagnetic waves through the electron atmosphere, which is semi-degenerate and inhomogeneous; to study the strange star cooling by taking into account the processes mentioned in (1)-(3). And other processes such as formation of color-flavor locked phase inside the star, chiral symmetry requirement in the boundary, will be included in the cooling calculations; to study the observational consequences of producing strange stars by accretion including how much gravitational and phase transition energy will be released through gravitational and electromagnetic waves. The possible connection between this process and [gamma]-ray bursts will be studied as well.

Project Title:	Time variation of fundamental physical constants in theories with extra-dimensions
Investigator(s):	Cheng KS
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003

Abstract:

To study in a systematically manner the possibility that the time variability of some fundamental physical constants (the elementary electric charge e, the speed of light c and the gravitational constant G) is due to the presence of the extra dimensions. More specifically, to consider the fundamental constants as some physical fields in a five-dimensional space-time and to examine the effects of such a hypothesis on the four-dimensional space-time.

Project Title:	Transient Gamma-ray Sources: Gamma-ray Bursts and Other Related Astrophysical Phenomena
Investigator(s):	Cheng KS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2004

Abstract:

To study (1) the evolution of the postburst fireball and their afterglows under different cases, e.g. effects of dense media, non-uniformity of media, geometry of jets (isotropic or highly collimated?) etc. We will compare the observed light curves and the time dependent multi-wave band spectra of the afterglows with model results. This information should provide very important clues to understand the origin of GRBs. (2) the inverse-Comption scattering in the internal shock can generate TeV photons, which are expected to form electron/positron pairs by collisions with inter-galactic infrared photons. Subsequent collisions between TeV pairs and cosmic microwave photons can cause delayed GeV-GRBs. The delay time scales and the spectra of delayed GeV-GRBs should be detectable for GLAST and provide vital information for the inter-galactic infrared photons as well as inter-galactic magnetic field. (3) some ideas, which we learn from GRBs, can be used to explain other transient gamma-ray phenomena, e.g. Anomalous X-Ray pulsars, Soft Gamma Repeaters and Microquasars, which exhibit some similar activities liek GBRs. For example, they all have jet-like features during the outburst states (flares) and their subsequent radiation processes could be explained in terms of internal/external shock mechanism, which are the mechanisms used to explain the radiation processes of GRBs.

Project Title:	High Energy Radiation from Pulsar and Pulsar Wind Nebula
Investigator(s):	Cheng KS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2005

Abstract:

There are three basic objectives of this project: (1) To study the magnetospheric radiation of a pulsar (2) To study the radiation resulting from the interaction between a pulsar wind and its surrounding medium (3) To study the relation between some unidentified high energy radiation point sources and pulsars

Project Title:	High Energy Emission from the Galactic Black Hole
Investigator(s):	Cheng KS
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	02/2006

Abstract:

Non-thermal high energy radiation emission within multi-pc scale from the center region of our galaxy has been observed. In particular very intense TeV photons are observed by various VHE experimental groups in the world. We believe that these high energy photons, especially TeV photon emission, are the result of a transient activity of the massive black hole SgrA*, which resides at the Galactic center. About hundred thousands of years ago, the black hole may have experienced in active phase by capturing a main sequence star and forming an accretion disk, temporarily behaving like an active galactic nuclear resemble to the activities observed in quasars. A powerful jet, which contains plenty of high speed protons, was launched during the process. These runaway protons interact with the dense ambient medium, producing high energy radiation emission through the decay of neutral pions. We believe that the total energy deposited in this way is large enough to account for observations. We will compare the model results with the observed data.

Project Title:	Relativistic collapse of neutron stars: gravitational radiation and gamma-ray emission
Investigator(s):	Cheng KS, Suen W.M., Chu MC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2006

Abstract:

(1) We propose to study the physical processes associated with collapsing neutron stars and aim to predict what gravitational wave signals and gamma-ray spectrum will be emitted from these collapsing neutron star systems. We will study two specific neutron star collapse scenarios. 1. When a neutron star in a low-mass X-ray binary accretes about 0.5 solar masses from its companion; it may undergo a phase-transition induced collapse. The collapsing neutron star may or may not evolve to a black hole; a denser compact object, e.g. a quark star, can be formed. The collapse leads to oscillations and an increase in the speed of rotation. The coupling between rotation and oscillations can produce strong gravitational waves. We will also investigate (non-axisymmetric) dynamical instabilities that may develop in the collapse process, in particular the so-called bar-mode instability. (2) Our preliminary Newtonian results indicate that the gravitational-wave signal sensitively depends on the equation of state used. In this project we will extend our previous Newtonian study to a fully relativistic study. The gravitational waveforms to be determined by the proposed study may be detected by the advanced Laser Interferometric Gravitational Wave Observatory (LIGO II), and our results may be used to put constraints on the underlying equation of state. Shock waves and differential rotation, which eventually will lead to high internal energy, will be developed during the collapse. Intense gamma-rays will be emitted from electron – positron annihilations emitted from the hot surface of the quark star. Our proposed study will allow us to test if the accretion induced phase-transition is a possible mechanism of gamma-ray bursts. 2. The merging of two neutron stars in a neutron star binary will lead to a collapse with high angular momentum. (3) The final object is likely a black hole – accretion disk system. It is well-known that the gravitational wave signals emitted from binary neutron star merger sensitively depend on the angular momentum in the system. In fact, how much matter is in the accretion torus outside the event horizon also sensitively depends on the angular momentum. We will calculate the neutrino emission from this hot degenerate accretion disk; subsequent neutrino – antineutrino annihilation can produce electron/positron jet. Although we may not able to answer the baryon contamination problem, we may be able to tell if such system can provide a powerful enough jet to produce the gamma-ray bursts and subsequent afterglow. If the energy content in the accretion disk is low for a wide range of angular momentum, it will challenge the scenario of neutron star merger as a possible central power engine of short gamma-ray bursts.(4) In summary, the objectives of this project are: • To study the gravitational radiations and gamma-ray emissions from phase-transition induced collapse of neutron stars and the physical processes during the collapse • To study how the inspiral parameters of neutron star – neutron star coalescence affect the gravitational waveforms and the matter distributions in the final black hole – accretion disk system

Project Title:	Radiation from Pulsars
Investigator(s):	Cheng KS
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2007

Abstract:

In this project we will study two topics related to strongly magnetized and rapidly rotating neutron stars. First we will study the structure of pulsar magnetosphere, the formation of acceleration region, pair creation and radiation processes. In particular, we would like to calculate the energy dependent light curves and phase dependent energy spectrum. We believe that these two predictions provide very important information for the emission regions, acceleration mechanisms and radiation processes in the magnetosphere of pulsars. We will also study the electrodynamical properties of the accelerators in the pulsar magnetosphere. We intend to construct a three dimensional pulsar accelerator model by including realistic current flow and pair creation process inside the accelerator. Secondly for pulsars with extremely strong magnetic field or so-called magnetars or anomalous X-ray pulsars, we believe that the acceleration cannot be the rotation power. Instead magnetic energy must be the origin of these high energy photons. We will calculate the Alfven wave acceleration process in the so-called closed magnetic field lines regions and compare that with the observed non-thermal spectrum by satellite called INTEGRAL as well as other high energy astronomical instruments.

List of Research Outputs

Becker W., Kramer M., Jessner A., Taam R.E., Jia J., Cheng K.S., Mignani R., Pellizzoni A., Luca A.D., Slowikowska A. and Caraveo P.A., A multiwavelength study of the pulsar PSR B1929+10 and its x-ray trail, The Astrophysical Journal. The American Astronomical Society, 2006, 645: 1421-1435.

Cheng K.S., Chernyshov D. and Dogel V., Annihilation emission from the galactic black hole, The Astrophysical Journal. The American Astronomical Society, 2006, 645: 1138-1151.

Cheng K.S. and Harko T.C., High energy emission from strange stars, The Seventh Pacific Rim Conference on Stellar Astrophysics. Astronomical Society of the Pacific, 2007, 362: 141-150.

Cheng K.S. and Usov V.V., Strangelets accelerated by pulsars in galactic cosmic rays, Physical Review D (Brief Reports). New York, The American Physical Society, 2006, 74: 127303: 1-4.

Huang Y., Lu Y., Wong Y.L. and Cheng K.S., A detailed study on the equal arrival time surface effect in gamma-ray burst afterglows, Chinese Journal of Astronomy and Astrophysics. National Natural Science Foundation of China, 2007, 7: 397-404.

Huang Y.F., Cheng K.S. and Lu Y., Theoretical interpretation of the optical afterglow of GRB 030329, Advances in Space Research. Amsterdam, Elsevier Ltd., 2007, 40: 1214-1217.

Jia J. and Cheng K.S., Phase-resolved spectra of the crab pulsar, The Seventh Pacific Rim Conference on Stellar Astrophysics. Astronomical Society of the Pacific, 2007, 362: 97-104.

Kang Y.W., Lee H.W., Cheng K.S. and Leung K.C., The Seventh Pacific Rim Conference on Stellar Astrophysics. Astronomical Society of the Pacific, 2007, 362.

Takata J., Chang H.K. and Cheng K.S., Polarization of high-energy emission from the crab pulsar, The Astrophysical Journal. The American Astronomical Society, 2007, 656: 1044-1055.

Wong Y.L., Huang Y.F. and Cheng K.S., Transient X-ray emission from normal galactic nuclei, Astronomy & Astrophysics. EDP Sciences, 2007, 472: 93-99.

Researcher : Cheng VKW

List of Research Outputs

Yu D., Zhang J., Cheng V.K.W., Beling C.D. and Fung S.H.Y., Doppler broadening of annihilation radiation spectroscopy study using Richardson-Lucy, Maximum Entropy and Huber methods, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3997-4000.

Researcher : Chernyshov D

List of Research Outputs

Cheng K.S., Chernyshov D. and Dogel V., Annihilation emission from the galactic black hole, The Astrophysical Journal. The American Astronomical Society, 2006, 645: 1138-1151.

Researcher : Cheung CH

List of Research Outputs

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Researcher : Cheung CK

List of Research Outputs

Cheung C.K., Wang R.X., Beling C.D., Djurisic A. and Fung S.H.Y., Positron beam study of indium tin oxide films on GaN, Journal of Physics: Condensed Matter. Bristol, IOP Publishing Limited, 2007, 19: 086204:1-10.

Cheung C.K., The construction of a focused low energy positron beam facility and its application in the study of various optoelectronic materials. Hong Kong, The University of Hong Kong, 2006, 1-194.

Gu Q., Ling F.C.C., Cheung C.K., Luo J., Chen X., Djurisic A., Brauer G., Anwand W., Skorupa W., Reuther H. and Ong H.C., Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment, In: S. Ashok, P. Kiesel, J. Chevallier, T. Ogino, Materials Research Society Spring Meeting 2007, 9-13 April 2007, San Francisco, Symposium F: Semiconductor Defect Engineering--Materials, Synthetic Structures, and Devices II. Materials Research Society, 2007, 994: F11-15.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Tam K.H., Cheung C.K., Leung Y.H., Djurisic A., Ling F.C.C., Beling C.D., Fung S.H.Y., Kwok W.M., Chan W.K., Phillips D.L., Ding L. and Ge W.K., Defects in ZnO nanorods prepared by a hydrothermal method, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 20865-20871.

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Wang R., Xu S.J., Beling C.D. and Cheung C.K., Response to "comment on influence of indium tin oxide thin-film quality on reverse leakage current of indium tin oxide/n-GaN Schottky contacts [Appl. Phys. Lett. 90, 046101 (2007)]", Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 046102-1.

Researcher : Cheung CK

List of Research Outputs

Researcher : Cheung KY

List of Research Outputs

Cai X., Cheung K.Y., Djurisic A. and Xie M.H., Growth of cubic and hexagonal InN nanorods, Materials Letters. Amsterdam, Elsevier B.V., 2007, 61: 1563-1566.

Cheung K.Y., Yip C.T., Djurisic A., Leung Y.H. and Chan W.K., Long K-doped titania and titanate nanowires on Ti foil and fluorine-doped tin oxide/quartz substrates for solar-cell applications, Advanced Functional Materials. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 17: 555-562.

Tong W.Y., Djurisic A., Xie M.H., Ng M.C.A., Cheung K.Y., Chan W.K., Leung Y.H., Lin H.W. and Gwo S., Metal phthalocyanine nanoribbons and nanowires, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 17406-17413.

Wang H., Yip C.T., Cheung K.Y., Djurisic A., Xie M.H., Leung Y.H. and Chan W.K., Titania-nanotube-array-based photovoltaic cells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 023508: 1-3.

Researcher : Cui X

Project Title:	The study on the conductance fluctuation of Carbon Nanotubes
Investigator(s):	Cui X
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2005

Abstract:

The objective of this proposed program is to experimentally study the nature of the conductance fluctuation observed on individual carbon nanotubes (CNT), which are a quasi one dimensional wire and are a promising candidate for nano-electronic materials.

Project Title:	Characterizing Carbon nanotube structures by Photo-Reflection
Investigator(s):	Cui X
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2006

Abstract:

The objective of this proposed program is to explore non-destructive techniques to identify individual carbon nanotube structures with photo-reflection experiments. Carbon nanotubes (CNTs have emerged as ideal materials for low dimensional physics studies and promising building blocks for nano electronics. They can be considered as carbon cylinders that are about a nanometer in diameter and a few hundred microns in length. They comprise a family of hundreds of structures, identified by distinct sets of two integers (n,m) which reflect various chirality and diameters, each having different electronic structures: these of mod(n–m,3)=0 are metallic, while the rest are semiconducting. The present weakness of the CNT field, however, is the fact that no one has yet found a synthesis of just one specific CNT structure (specific diameter and chirality). The structure of individual carbon nanotubes in such carbon nanotube devices as CNT field effect transistors and CNT field emitters are kind of stochastic. Namely, we have great difficulty in relating series of data on individual CNTs to specific material structures. Therefore the structure characterizing is important to understand the physics inside. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (STM), Resonant Raman scattering, and photoluminescence have been exploited in structure characterization. Among them, TEM and STM produce precise physical images of individual CNT at Angstrom resolution. But they cannot in situ study the CNTs and sample processing and ultra high vacuum (UHV) environments are necessary. Besides these characterization techniques are destructive for CNTs devices. Resonanant raman scattering probes two distinct phonon modes on CNTs: the radial breathing mode (RBM) in a range of 100 to 300 cm-1 and the G mode at around 1586 cm-1. The RBM mode frequency is a linear function of the diameter of the tubes, and can be used to determine the size distribution of a CNT sample. The G mode spectra lineshape depends on whether the CNT is semiconducting or metallic, and also on its diameter, temperature and doping. The intensity of Raman scattering, especially the ratio of stoke mode intensity vs. anti-stoke mode, is very sensitive to incident laser energy and polarization. These features make resonant Raman scattering a powerful tool for the precise identification of CNTs and the study of their electronic structures. However, there is one drawback to using Raman scattering as a CNT characterization tool. The Raman signal is so weak that the incident laser has to be adjusted to resonate with the CNT sub-band transition for the Raman signal to become detectable. A tunable laser Raman measurement is both expensive and difficult to achieve. Photoluminescence characterizing technique is to locate the photoluminescence spectrum of individual CNTs in the structure map which collects spectra from all identified CNTs. As the photoluminescence is much stronger than Raman scattering, it simplifies the experimental setup. It however has several significant drawbacks: First CNTs are very susceptible to their environments, and as the metallic tubes and substrates used with semiconducting CNTs will easily quench their fluorescence. CNTs must be encapsulated with micelle by mechanical and chemical treatments to avoid quenching their photoluminescence. These processes make in situ study infeasible. Second, nearly one third of CNTs are metallic and are unable to photoluminescece. As well, the photoluminescence spectra of many CNTs lie in Near infra-red range, where detection apparatus in infra-red range are always problematic. In this project, we propose to characterize individual CNT structures by studying the photo-reflection on individual CNTs. The principle bases on the fact that each identical structured CNT has its own specific electronic structure, depending on its diameter and chirality. And the dielectric constant is mainly determined by electronic structures. So we plan to obtain the dielectric constant on individual CNTs and then to locate the electronic structure and therefore locate the CNT structure.

Project Title:	An optical study of electronic structures of carbon nanotubes
Investigator(s):	Cui X
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	08/2006

Abstract:

(1) To build a comprehensive, nondestructive optical measurement system in order to accomplish micro-Raman characterization, photo induced conductance, photoluminescence and electroluminescence spectroscopy at the single carbon nanotube level. (2) To study the excitonic effect, exciton binding strength, electron-photon coupling, and structure dependence of luminescence spectrum on identified single carbon nanotubes by applying micro-Raman characterization, photo induced conductance, photoluminescence and electroluminescence spectroscopy to single carbon nanotubes.(3) The study will elucidate the optical and electric properties of single nanotubes, and will benefit not only carbon nanotube research but also the entire field of the low dimensional physical sciences and nanotechnology.

Project Title:	Detection of pure spin currents
Investigator(s):	Cui X
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2007

Abstract:

The project aims to explore an experimental technique to detect the pure spin current, which is one of the key components to realization of spintronics. Electrons have a quantum state of spin as well as electric charges. Spintronics or spin electronics is known as a emergent technology which exploit the quantam state of electron spin in addition to making use of electron charges. In order to make a spintronic device, the primary requirement is to have a system that can generate a current of spin polarized electrons, and a system that is sensitive to the spin polarization of the electrons. A current of spin polarized electrons, know as spin current refers to the spin aligned electron flowing: for example, spin ‘up’ electron moving towards the left and spin ‘down’ electrons moving opposite. The generation of spin current can be realized by spin electron injection from ferromagnetic materials, 1 by external magnetic field, 2 3 4 and by spin-orbital interaction. 5 6 7. The electric charge flowing is not necessary as a result of opposite moving electric current. The spin current without carrying net electric charge flow is generally referred to pure spin current. The detection of pure spin current has been challenging. A few of achievements to spin current detection were reported recently. One of them is to detect spin current by spin Hall effect via two independent experiments: Accumulation of “spin up” and “spin down” electrons at opposite edges of the conducting channel of GaAs in bulk form and in two dimensional a electron gas (2DEG) system under a DC bias was observed with Kerr rotation microscopy by Awschalom group.8 , and with electroluminescence by Cambridge group9. A direct measurement of the spinned electron flow has been generated with optical inject and been observed with spatial resolved photoluminescence 7 10. Although the progress is impressive, one fundamental obstacle to spintronics devices exists. The present techniques of spin current detection all are based on the complicated optical spectroscopy. For application oriented research purpose, electronic signal raised from spin current is of great interest. The current efforts however do not discover any electric phenomena related to pure spin current yet. In this application, we propose a novel experiment to detect pure spin currents in 2DEG. The electric phenomena related to pure spin currents are focused. The proposed study will try to explore the physics in spin current in 2DEG system and will aim to a new solution to spin current based devices. 1 A. Brataas, Y. Tserkovnyak, G. E. W. Bauer, and B. I. Halperin, Physical Review B 66, 060404 (2002). 2 Q.-f. Sun, H. Guo, and J. Wang, Physical Review Letters 90, 258301 (2003). 3 E. R. Mucciolo, C. Chamon, and C. M. Marcus, Physical Review Letters 89, 146802 (2002). 4 K. W. Susan, R. M. Potok, C. M. Marcus, and V. Umansky, (APS, 2003), Vol. 91, p. 258301. 5 J. Nitta, T. Akazaki, H. Takayanagi, and T. Enoki, Physical Review Letters 78, 1335 (1997). 6 R. D. R. Bhat and J. E. Sipe, Physical Review Letters 85, 5432 (2000). 7 J. Hubner, W. W. Ruhle, M. Klude, D. Hommel, R. D. R. Bhat, J. E. Sipe, and H. M. v. Driel, (APS, 2003), Vol. 90, p. 216601. 8 Y. K. Kato, R. C. Myers, A. C. Gossard, and D. D. Awschalom, 2004), Vol. 306, p. 1910. 9 J. Wunderlich, B. Kaestner, J. Sinova, and T. Jungwirth, (APS, 2005), Vol. 94, p. 047204. 10 J. S. Martin, L. S. Arthur, R. D. R. Bhat, N. Ali, J. E. Sipe, and H. M. v. Driel, (APS, 2003), Vol. 90, p. 136603.

List of Research Outputs

Cui X., Shen S.Q., Li J., Ji Y., Ge W.K. and Zhang F.C., Observation of electric current induced by optically injected spin current, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 242115: 1-3.

Researcher : Dai D

List of Research Outputs

Dai D., Xu S.J., Shi S., Xie M.H. and Che C.M., Observation of both second-harmonic and multiphoton-absorption-induced luminescence in ZnO, IEEE Photonics Technology Letters. IEEE, 2006, 18: 1533-1535.

Li Q., Xu S.J., Li G., Dai D. and Che C.M., Two-photon photoluminescence and excitation spectra of InGaN/GaN quantum wells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 011104: 1-3.

Researcher : Dai X

Project Title:	The studies on the dynamical mean field theory and its application in the first principle calculation of the strongly correlated materials
Investigator(s):	Dai X, Zhang FC, Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2005

Abstract:

1) To develop several fast impurity solvers which can be used in the LDA+DMFT calculation for the Mott insulators, where the effective quantum impurity model is close to the atomic limit. 2) Apply the LDA+DMFT method to do the first principle calculation for the typical anti-ferromagnetic materials, such as $MnF_2$ and $MnO$. 3) To develop a impurity solver in the strong local interaction but with non integer particle filling.

Project Title:	The optical response of the semiconductor quatum well structure carrying non-zero spin current
Investigator(s):	Dai X
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2006

Abstract:

Recently the spintronics, whose main task is to study the transport and manipulation of the spin degree of freedom in solids, become a very hot field of the condensed matter physics. One of the big problem of the spintronics is how to generate and detect spin current, which can transport spin signals from one place to another. Unlike the charge current, which is very easy to detect, the pure spin current is very hard to detect. About two years ago, the study of spin Hall effect (SHE), in which an electric field induces a transverse spin current, has recently evolved into a subject of intense research. The intrinsic SHE was proposed by Murakami et al. in p-type semiconductor of a Luttinger Hamiltonian and by Sinova in 2-dimensional (2D) electron systems with Rashba spin-orbit coupling. Their works have generated a lot of theoretical activities. Current theoretical understanding is that the intrinsic SHE does not survive in the diffusive transport in the thermodynamic limit for the 2D Rashba electron system in the absence of strong magnetic fields but the effect appears to be robust in the 2D hole gases p-doped bulk semiconductors and the modified Rashba coupling case. The earlier theoretical work on the extrinsic SHE is associated with the impurity scattering, such as the skew scattering and the side jump processes. On the experimental side, there have been two groups reporting the observation of SHE. Kato et.al. used Kerr rotation microscopy to detect and image electrically induced electron-spin polarization near the edge of a n-type semiconductor channel. The effect was suggested to be extrinsic based on the weak dependence on crystal orientation for the strained samples. Very recently, Sih et al. have reported spatial imaging of the SHE and current-induced polarization in 2D electron gases. Wunderlich et al. observed the SHE in 2D hole system with spin-orbit coupling, and interpreted the effect to be intrinsic. Therefore it will be very important if we can propose a new way to measure the spin current by out theoretical study. Since both of the two experimental on the possible spin Hall effects are done by the optical measurement. The Kerr effect was used in Kato's experiment and photo luminescence was used in Wunderlich's experiment. On the other hand, the optical properties of the semiconductors with strong spin-orbital coupling itself is a very interesting problem which has been studies extensively in the past twenty years, because it shed light on how to manipulate spin by the optical way. Based on the above research background, we plan to carry out the theoretical studies on the optical properties of the semiconductor quantum wells with the strong spin-orbital coupling. In the study, we will focus on two very fundamental problems. One is that is there any new physical phenomena in the optical absorption or emission which is induced by the spin-orbital coupling? Since we know that the spin Hall effect in the 2 dimensional electron (hole) gas is induced by the non-trivial Berry phase in the momentum space, one would ask how does this kind of Berry phase manifest itself in the optical absorption or emission? The second interesting problem that we are currently working with is that what is the optical response for a quantum well sample which is carrying a non-zero spin current? Does the spin current feature manifest itself in the optical response? If so, can we develop a new method to measure the spin current? In this proposal, we plan to study the optical response of the semiconductor quantum well with strong spin-orbital coupling. Using the kp method which has been developed for 40 years, we are going to study the absorption of the circlely polarized (CP) light by the quantum well structure. As discovered already by many groups, the absorption of the CP light will not generate any net charge current when the light is applied perpendicular to the xy-plane. Here we are going to calculate the change of the absorption rate of the CP light induced by a external static electric field. Because of the spin Hall effect, the electron (hole) spin which is originally lying within the plane will tilt out of the plane, which will affect the absorption rate of the CP light. We will study if such an effect will result in a non-zero charge current along the transverse direction within the plane. If so, this charge current is purely caused by the external electric field and is totally a new effect in semiconductor physics. Another very important issue is that is it possible to measure the spin current itself rather than the spin accumulation at the edge by the optical method? This problem can also be answered by our study. We expect that the presence of the spin current will affect the cross section of the optical absorption or emission processes. And thus provide a new optical method to measure the spin current directly. Since up to now, there is no method which can measure the spin current directly, our theoretical research will be extremely significant in the area of the spintronics.

Project Title:	The study on the metal insulator transition in the multi-band system using the dynamical mean field theory
Investigator(s):	Dai X, Zhang FC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2006

Abstract:

(1) We plan to develop very efficient parallised codes of the exact diagonization (ED) which will be used as a impurity solver for dynamical mean field theory (DMFT). The exact diagonization is a quite reliable impurity solver for DMFT at zero temperature. It has been used commonly in the Mott transition problem in multi-band Hubbard model. The key issue of the ED solver is to use as many sites as possible to simulate the heat bath. As we learnt from the literature, we expect to get the satisfactory results using three or four sites for the heat bath. We will develop very efficient parallised ED codes for the powerful pc cluster in HKU named hpcpower. (2) With the ED impurity solver developed above, we will study the phase diagram of the three-band Hubbard model using DMFT. We will study how the phase diagram will change with the Hund's rule coupling and the crystal field splitting. As we will discuss in detail late, a new type of orbital selective Mott transition which is driven by crystal field will be studied in detail. Our research work will shed light on many interesting phenomena in the transition metal oxides with partially filled t2g orbits.(3) The transition between Mott insulator and band insulator will be studied in detail using DMFT. We will answer the following questions. If such a transition from Mott insulator to band insulator happens directly or not? If there is a new phase in between, is it a metallic phase or another type of insulator phase? We expect that the Hund’s rule coupling will also play a very important role here.

List of Research Outputs

Yao Y.G., Liang Y.C., Xiao D., Niu Q., Shen S.Q., Dai X. and Fang Z., Theoretical evidence of the Berry-phase mechanism in anomalous Hall transport: First-principles studies of CuCr₂Se₄₋_xBr_x, Physical Review B (Rapid Communications). New York, The American Physical Society, 2007, 75: 020401: 1-4.

Researcher : Djurisic A

Project Title:	Structural, electrical, and optical properties of organic/inorganic nanocomposites for optoelectronic applications
Investigator(s):	Djurisic A, Chan WK
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004

Abstract:

To study : (1) the fabrication and/or surface modifications of inorganic nanostructures; (2) the fabrication of nanocomposite films containing one or more types of nanostructures; (3) the study of structural, electrical, and optical properties of nanocomposite films; (3) the application of nanocomposite films to organic light emitting diodes and organic solar cells.

Project Title:	Optical properties of ZnO nanostructures
Investigator(s):	Djurisic A, Chan WK
Department:	Physics
Source(s) of Funding:	France/Hong Kong Joint Research Scheme - Travel Grants
Start Date:	01/2006

Abstract:

1) Fabrication and charaterization of the optical properties of ZnO nanostructures; 2) Investigation of the effect of surface functionalization on the optical properties

Project Title:	Dye- and polymer sensitized solar cells based on novel nanostructured semiconductor layers
Investigator(s):	Djurisic A
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2006
Completion Date:	12/2006

Abstract:

In order to maintain a sustainable environment, there is a high demand to produce inexpensive renewable energy sources. Therefore, the development of low production cost solar cells is of particular interest. Organic materials have an important advantage of enabling fabrication of devices on large are and flexible substrates, using inexpensive solution processing techniques. Among different types of organic solar cells, dye-sensitized cells typically have the highest power conversion efficiency, which is ~10%. A dye-sensitized solar cell typically consists of a porous TiO2 layer infiltrated with dye sensitizer molecules. To study the factors limiting the efficiency of these cells, as well as to try to improve the charge transport and reduce recombination of generated carriers, different nanostructured semiconductors (ZnO, SnO2) in addition to TiO2 are intensively investigated. In addition, polymer sensitized solar cells are being studied in order to achieve good performance solid state devices without liquid electrolyte. In this project, different nanostructured metal oxides will be prepared and their application to the dye- and polymer-sensitized solar cells will be investigated. Objectives: o Fabrication of dye-sensitized and polymer-sensitized solar cells based on novel metal oxide nanostructured layers o Study of the influence of nanostructured layer morphology on the solar cell performance o Optimizing the architecture of the solar cells based on novel nanostructured layers to achieve improved device performance.

Project Title:	Nanomaterial homojunctions and heterostructures for photovoltaic applications
Investigator(s):	Djurisic A
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	02/2007

Abstract:

In recent years, nanomaterials have attracted lots of attention due to their great potential for applications in various optoelectronic devices with improved performance. In particular, one-dimensional nanostructures are of great interest for solar cell applications [1,2]. The important advantage of one dimensional nanostructures is improved charge transport through a single crystalline nanowire compared to a layer consisting of nanoparticles [1]. For example, mobility in single crystal rutile TiO2 (1 cm2/Vs ) is two orders of magnitude higher than that of porous titania layer [3]. In addition, other nanomaterials such as GaN/AlN/AlGaN radial nanowire heterostructrures show very high mobilities (~3100 cm2/Vs) [4]. However, the efficiency of nanowire based solar cells is still considerably lower than that of the best nanoparticle TiO2 solar cells (1.5% for ZnO nanowires [1] vs. 10% for TiO2 nanoparticle based cell [5]). One reason for this is that surface area of nanowire-based cells is lower than the surface area of nanoparticle based cells [1]. Another reason is the problem of dye-loading for Ru-complexes when a different material is substituted for TiO2. For example, ZnO becomes unstable in acidic solutions, so that it dissolves in dye-loading solution due to presence of protons derived from Ru-complexes [6]. Although some dyes such as N719 may result in successful sensitization of ZnO, efficiencies are still lower than those achieved for TiO2 (4.1%) [6]. In addition, no dye-sensitized solar cells based on nitride materials have been reported. In this project, nanomaterial homojunctions and heterostructures with increased surface area and improved dye loading will be fabricated. The surface area of the nanowires will be increased by radial nanorod growth and/or roughening the surface of the nanowires. Both homojunctions (TiOx/TiOx, ZnO/ZnO) and heterojunctions (ZnO/TiOx, TiOx/ZnO, GaN/ZnO etc.) will be studied. For the improved dye-loading, coaxial heterostructures will be considered in order to achieve efficient electron transport through the core nanowire and efficient dye attachment and electron injection into outer layer.Objectives:1. Fabrication of different nanomaterial homojunctions (TiOx/TiOx, ZnO/ZnO) and heterostructures (ZnO/TiOx, GaN/TiOx, etc.)2. Study of the structural and optical properties of the fabricated nanomaterial junctions3. Application of fabricated nanostructures to solar cells [1] M. Law, L. E. Greene, J. C. Johnson, R. Saykally, P. D. Yang, Nat. Mater. 2005, 4, 455.[2] G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, C. A. Grimes, Nano Lett. 2006, 6, 215.[3] E. Hendry, M. Koerberg, B. O'Regan, M. Bonn, Nano Lett. 2006, 6, 755.[4] Y. Li, J. Xiang, F. Qian, S. Gradecak, Y. Wu, H. Yan, H. Yan, D. A. Bloom, C. M. Lieber, Nano Lett. 2006, 6, 1468.[5] B. O'Regan and M. Grätzel, Nature 1991, 353, 737.[6] K. Kakiuchi, E. Hosono, S. Fujihara, Journal of Photochemistry and Photobiology A: Chemistry 2006, 179, 81.

List of Research Outputs

Brauer G., Anwand W., Grambole D., Skorupa W., Hou Y., Andreev A., Teichert C., Tam K.H. and Djurisic A., Non-destructive characterization of vertical ZnO nanowire arrays by slow positron implantation spectroscopy, atomic force microscopy, and nuclear reaction analysis, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 195301: 1-8.

Cai X., Djurisic A. and Xie M.H., GaN nanowires: CVD synthesis and properties, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 984-989.

Cai X., Cheung K.Y., Djurisic A. and Xie M.H., Growth of cubic and hexagonal InN nanorods, Materials Letters. Amsterdam, Elsevier B.V., 2007, 61: 1563-1566.

Chan C.P., Gao J., Yue T.M., Surya C., Ng M.C.A., Djurisic A., Liu P.C.K. and Li M., Study of laser-debonded GaN LEDs, IEEE Transactions on Electron Devices. IEEE, 2006, 53: 2266-2272.

Chan S.W., Barille R., Nunzi J.M., Tam K.H., Leung Y.H., Chan W.K. and Djurisic A., Second harmonic generation in zinc oxide nanorods, Applied Physics B. Berlin, Springer-Verlag, 2006, 84: 351-355.

Chen X., Ling F.C.C., Djurisic A., Brauer G., Anwand W., Skorupa W. and Reuther H., Influence of hydrogen peroxide treatment on Au/n-ZnO contact, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Cheung C.K., Wang R.X., Beling C.D., Djurisic A. and Fung S.H.Y., Positron beam study of indium tin oxide films on GaN, Journal of Physics: Condensed Matter. Bristol, IOP Publishing Limited, 2007, 19: 086204:1-10.

Cheung K.Y., Yip C.T., Djurisic A., Leung Y.H. and Chan W.K., Long K-doped titania and titanate nanowires on Ti foil and fluorine-doped tin oxide/quartz substrates for solar-cell applications, Advanced Functional Materials. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 17: 555-562.

Djurisic A., Leung Y.H., Tam K.H., Hsu Y.F., Ding L., Ge W.K., Zhong Y.C., Wong K.S., Chan W.K., Tam H.L., Cheah K.W., Kwok W.M. and Phillips D.L., Defect emissions in ZnO nanostructures, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 095702: 1-8.

Djurisic A. and Leung Y.H., Optical properties of ZnO nanostructures, Small. Weinheim, WILEY-VCH Verlag GmbH & Co., 2006, 2: 944-961.

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Djurisic A., Outstanding Young Researcher, The University of Hong Kong. 2006.

Gu Q., Ling F.C.C., Cheung C.K., Luo J., Chen X., Djurisic A., Brauer G., Anwand W., Skorupa W., Reuther H. and Ong H.C., Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment, In: S. Ashok, P. Kiesel, J. Chevallier, T. Ogino, Materials Research Society Spring Meeting 2007, 9-13 April 2007, San Francisco, Symposium F: Semiconductor Defect Engineering--Materials, Synthetic Structures, and Devices II. Materials Research Society, 2007, 994: F11-15.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Hsu Y.F., Djurisic A. and Tam K.H., Morphology and optical properties of ZnO nanostructures grown under zinc and oxygen-rich conditions, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2007, 304: 47-52.

Kwok K.P.W.H., Leung K.M.Y., Cheng S.H., Poon W.L., Lam P.K.S., Flauhaut E. and Djurisic A., Population effects of three common nanomaterials to the copepod Tigriopus japonicus, The 5th international Conference on Marine Pollution and Ecotoxicology, 3-6 June 2007, City University of Hong Kong, Hong Kong. 2007.

Kwok W.M., Djurisic A., Leung Y.H., Li D., Tam K.H., Phillips D.L. and Chan W.K., Influence of annealing on stimulated emission in ZnO nanorods, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 183112: 1-3.

Lu A.W., Chan J., Rakić A.D., Ng M.C.A. and Djurisic A., Optimization of microcavity OLED by varying the thickness of multi-layered mirror, Optical and Quantum Electronics. Springer, 2006, 38: 1091-1099.

Man K.K.Y., Tse C.W., Cheng K.W., Djurisic A. and Chan W.K., Fabrication of photovoltaic cells using rhenium diimine complex containing polyelectrolytes by the layer-by-layer electrostatic self-assembly method, Journal of Inorganic and Organometallic Polymers and Materials. Springer Science, 2007, 17: 223-233.

Ng K.Y., Muley A.A., Chan Y.F., Ng M.C.A., Djurisic A. and Ngan A.H.W., Highly facetted metallic zinc nanocrystals fabricated by thermal evaporation, Materials Letters. Amsterdam, Elsevier B.V., 2006, 60: 2423-2427.

Tam K.H., Cheung C.K., Leung Y.H., Djurisic A., Ling F.C.C., Beling C.D., Fung S.H.Y., Kwok W.M., Chan W.K., Phillips D.L., Ding L. and Ge W.K., Defects in ZnO nanorods prepared by a hydrothermal method, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 20865-20871.

Tong W.Y., Djurisic A., Xie M.H., Ng M.C.A., Cheung K.Y., Chan W.K., Leung Y.H., Lin H.W. and Gwo S., Metal phthalocyanine nanoribbons and nanowires, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 17406-17413.

Tong W.Y., Djurisic A., Ng M.C.A. and Chan W.K., Synthesis and properties of copper phthalocyanine nanowires, Thin Solid Films. Amsterdam, Elsevier B.V., 2007, 515: 5270-5274.

Tse C.W., Chan W.K. and Djurisic A., Hyperbranched polymer as surface modifier for nanosized zinc oxide tetrapods, American Chemical Society 232nd National Meeting, San Francisco, U.S.A., September 10-14, 2006.

Tse C.W., Man K.K.Y., Cheng K.W., Mak S.K., Chan W.K., Yip C.T., Liu Z. and Djurisic A., Layer-by-layer deposition of rhenium-containing hyperbranched polymers and fabrication of photovoltaic cells, Chemistry-A European Journal. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 13: 328-335.

Tse C.W., Chan W.K. and Djurisic A., Modification of ZnO Tetrapod and Nanorod Surfaces by the Layer-by-Layer Deposition Process, 90th Canadian Chemistry Conference, Winnipeg, Canada, May 28-30, 2007.

Tse C.W., Leung Y.H., Tam K.H., Chan W.K. and Djurisic A., Tailoring and modifications of a ZnO nanostructure surface by the layer-by-layer deposition technique, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 3563-3568.

Wang H., Yip C.T., Cheung K.Y., Djurisic A., Xie M.H., Leung Y.H. and Chan W.K., Titania-nanotube-array-based photovoltaic cells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 023508: 1-3.

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Wong H.L., Mak S.K., Chan W.K. and Djurisic A., Efficient photovoltaic cells with wide photosensitization range fabricated from rhenium benzathiazole complexes, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 081107: 1-3.

Wong H.L., Mak S.K., Leung Q.Y., Chan W.K. and Djurisic A., Use of Sublimable Rhenium Diimine Complexes as Photosensitizers in Bulk Heterojunction Photovoltaic Devices, The 7th International Symposium on Advanced Organic Photonics, Angers, France, June 13-15, 2007.

Researcher : Dogel V

List of Research Outputs

Cheng K.S., Chernyshov D. and Dogel V., Annihilation emission from the galactic black hole, The Astrophysical Journal. The American Astronomical Society, 2006, 645: 1138-1151.

Researcher : Fung PCW

Project Title:	Development of a novel natural antioxidant with strong anti-aging and protective properties for skin
Investigator(s):	Fung PCW, Shen J
Department:	Medicine
Source(s) of Funding:	Seed Funding Programme for Applied Research
Start Date:	07/2002

Abstract:

To develop a novel antioxidants from herbal products which can scavenge superoxide, hydroxyl and lipid peroxide free radicals in skin.

Project Title:	Roles of plasma membrane cholesterol homeostasis in regulating neuronal oxidative damage of ischemic stroke
Investigator(s):	Fung PCW, Shen J
Department:	Medicine
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003

Abstract:

To understand the roles of plasma membrane cholesterol homeostasis in protecting neuronal cells from oxidative damage during ischemic stroke.

Project Title:	High level brain activity studies and applications
Investigator(s):	Fung PCW, Chang C, Chan FHY
Department:	Medicine
Source(s) of Funding:	NSFC/RGC Joint Research Scheme
Start Date:	01/2004

Abstract:

To better understand and utilize the functioning of the brain.

List of Research Outputs

Researcher : Fung S

Project Title:	Study of Particle Irradiation Induced Defects in Gallium Nitride
Investigator(s):	Fung SHY
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004
Completion Date:	09/2006

Abstract:

To systematically study the particle irradiation induced defects in GaN. Irradiation with electrons, neutrons, and protons is known to damage semiconductor materials by causing atomic displacement and/or ionization. The type and size of defects created depend on the energy, mass, charge, and fluency of the irradiating particles. Thus various defects such as mono-vacancy, divacancy, interstitial and antisite with different generation rates in samples irradiated with different particles may be studied; to compare the properties of defects created by the three different irradiation particles mentioned above.

Researcher : Fung SHY

Project Title:	Study of Particle Irradiation Induced Defects in Gallium Nitride
Investigator(s):	Fung SHY
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004
Completion Date:	09/2006

Abstract:

List of Research Outputs

Cheung C.K., Wang R.X., Beling C.D., Djurisic A. and Fung S.H.Y., Positron beam study of indium tin oxide films on GaN, Journal of Physics: Condensed Matter. Bristol, IOP Publishing Limited, 2007, 19: 086204:1-10.

Ding L., Chen T.P., Wong J.I., Yang M., Liu Y., Ng C.Y., Liu Y.C., Tung C.H., Trigg A.D. and Fung S.H.Y., Dielectric functions of densely stacked Si nanocrystal layer embedded in SiO₂ thin films, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 251910:1-3.

Ding L., Chen T.P., Liu Y., Yang M., Wong J.I., Liu Y.C., Trigg A.D., Zhu F.R., Tan M.C. and Fung S.H.Y., Influence of nanocrystal size on optical properties of Si nanocrystals embedded in SiO₂ synthesized by Si ion implantation, Journal of Applied Physics. New York, American Institute of Physics, 2007, 101: 103525:1-6.

Ding L., Chen T.P., Yang M., Wong J.I., Liu Y., Yu S.F., Zhu F.R., Tan M.C., Fung S.H.Y., Tung C.H. and Trigg A.D., Photon-induced conduction modulation in SiO₂ thin films embedded with Ge nanocrystals, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 103102: 1-3.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Hui C.W., Zhang J., Zhou T., Ling F.C.C., Beling C.D., Fung S.H.Y., Brauer G., Anwand W. and Skorupa W., Positron annihilation study of hydrothermal grown n-type zinc oxide, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Liu Y., Chen T.P., Lau H.W., Wong J.I., Ding L., Zhang S. and Fung S.H.Y., Charging effect on current conduction in aluminum nitride thin films containing Al nanocrystals, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 123101: 1-3.

Liu Y., Chen T.P., Ding L., Zhang S., Fu Y.Q. and Fung S.H.Y., Charging mechanism in a SiO₂ matrix embedded with Si nanocrystals, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 096111:1-3.

Liu Y., Chen T.P., Ng C.Y., Ding L., Zhang S., Fu Y.Q. and Fung S.H.Y., Depth profiling of charging effect of Si nanocrystals embedded in SiO2: A study of charge diffusion among Si nanocrystals, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 16499-16502.

Liu Y., Chen T.P., Ding L., Yang M., Wong J.I., Ng C.Y., Yu S.F., Li Z.X., Yuen C., Zhu F.R., Tan M.C. and Fung S.H.Y., Influence of charge trapping on electroluminescence from Si-nanocrystal light emitting structure, Journal of Applied Physics. New York, American Institute of Physics, 2007, 101: 104306: 1-4.

Nahid F., Beling C.D. and Fung S.H.Y., Temperature dependence study of positronium formation in high density polyethylene by positron annihilation lifetime spectroscopy, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3751-3754.

Ng C.Y., Chen T.P., Zhao P., Ding L., Liu Y., Tseng A.A. and Fung S.H.Y., Electrical characteristics of Si nanocrystal distributed in a narrow layer in the gate oxide near the gate synthesized with very-low-energy ion beams, Journal of Applied Physics. New York, American Institute of Physics, 2006, 99: 106105:1-3.

Panda S., Panda B.K. and Fung S.H.Y., Effect of conduction band nonparabolicity on the dark current in a quantum well infrared detector, Journal of Applied Physics. New York, American Institute of Physics, 2007, 101: 043705:1-8.

Tam K.H., Cheung C.K., Leung Y.H., Djurisic A., Ling F.C.C., Beling C.D., Fung S.H.Y., Kwok W.M., Chan W.K., Phillips D.L., Ding L. and Ge W.K., Defects in ZnO nanorods prepared by a hydrothermal method, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 20865-20871.

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Wang R., Xu S.J., Shi S., Beling C.D., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au/GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 143505: 1-3.

Yang M., Chen T.P., Wong J.I., Ng C.Y., Liu Y., Ding L., Fung S.H.Y., Trigg A.D., Tung C.H. and Li C.M., Charge trapping and retention behaviors of Ge nanocrystals distributed in the gate oxide near the gate synthesized by low-energy ion implantation, Journal of Applied Physics. New York, American Institute of Physics, 2007, 101: 124313: 1-5.

Yu D., Zhang J., Cheng V.K.W., Beling C.D. and Fung S.H.Y., Doppler broadening of annihilation radiation spectroscopy study using Richardson-Lucy, Maximum Entropy and Huber methods, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3997-4000.

Researcher : Gao J

Project Title:	Preparation of epitaxial YBa₂Cu₃O_y thin films on silicon with a double buffer of Eu₂CuO₄/YSZ
Investigator(s):	Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2002

Abstract:

The project proposes to reveal the feasibility of applying a double buffer EuCuO(ECO)/YSZ to improve the growth of YBCO on Si. The synthesis process, resultant structural properties and their relation to superconductivity of YBCO films will be investigated. In addition, their crystalline and superconductivity, as well as the interfaces will be systematically studied.

Project Title:	Current induced deduction on the peak resistance of perovskite transition metal oxides
Investigator(s):	Gao J
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003
Completion Date:	03/2007

Abstract:

To study the influence of a transport current in the peak resistance of perovskite transition metal oxides.

Project Title:	Opto-electric response and light excitation in heteroepitaxial thin films of R1-xAxMnO3 perovskite oxides
Investigator(s):	Gao J
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2005
Completion Date:	12/2006

Abstract:

The electronic states in perovskite oxides R1-xAxMnO3, which are not completely understood currently, play the dominant role in determining the material properties. The motivation of the research lies in the opto-electronic response in heteroepitaxial thin films of these compounds. The main objective is to reveal the nature of giant electroresistance (ER) and to get a better understanding of the mechanism that account for the peculiar nonlinear electronic transport. Our efforts will be focused at the electron-phonon interaction and the effects induced by optical excitation in these materials, as well as the modulation process of a light/field on the coexistence of multiphases in different systems. In particular, the following pertinent scientific and technical issues will be addressed: • Growth and structural characterization of heteroepitaxial films of various perovskite manganites. • Electronic states and optical characterization in these heteroepitaxial structures. • The opto-electronic responses and giant ER effects under an optical or field excitation. Effort will be also made to explore the feasibility for device applications, though it is not the main objective. This part of study explore how the applied field affects the properties of these material in hoping to shed light on the physical mechanisms, which are difficult to understand using conventional research scheme. Interaction between a material and external excitation is always a hot subject in physics society. Our recent study has shown that a current with a high density can induce a giant ER in the ABO3 thin films. With the incorporation of optical excitation into the experiment, free carriers can be excited in the materials and, likely, the MI transition will be influenced. Our research will aim at the dynamical process of the way that electrons are excited and how the photon-generated electrons interact with Mn ions. Since the magnetic properties of R1-xAxMnO3 is closely related to holes, optical excitation can serve as a unique laboratory in which many of the material properties can be studied.

Project Title:	Normal and abnormal giant electroresistance induced by currents in epitaxial thin films of mixed-valent manganite oxides
Investigator(s):	Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

To systematically investigate the current induced giant ER effect in wide range of epitaxial thin films of mixed-valent manganite oxides; to study the nature of the novel metastable state introduced subsequently by applying a large current, i.e. the abnormal ER effect; try to understand the physical mechanism behind these experimental observations.

Project Title:	Magnetically tunable heterojunctions constructed with manganite perovskites
Investigator(s):	Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2006

Abstract:

The main objective of this project is to explore the feasibility for developing functional p-n heterojunctions from manganite perovskites, which could be magnetically tunable. As the influence of the giant MR and ER on behavior of these heterojunctions has not been well understood, our study would be very likely to emerge interesting results and may exhibit unexpected new properties or phenomena

Project Title:	Opto-electric response in heteroepitaxial junctions composed of transition metal perovskites
Investigator(s):	Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2007

Abstract:

(1) To study the opto-electronic response of heteroepitaxial p-n junctions of perovskite manganites. Heteroepitaxial junctions with a well-defined interface are essential for the proposed study. A good control over the crystal perfection, epitaxial orientation, as well as a clear interface at atomic level in multiplayer structures will be pursued. The photo-electronic interaction and influence of optical irradiation on the I-V characteristics and transport will be studied with different wavelengths and light intensity. This research aims at obtaining dynamic light control of electrical transport in various hetero-structures. (2) To investigate the electronic states and boundary resistance under an optical or e-field excitation. This study can explore how the applied optical or electric field affects the properties of the material in hoping to shed light on the physical mechanisms, which are difficult to understand using conventional research scheme. Our recent study has shown that a current with a high density can induce a giant ER in the ABO3 films. With the incorporation of optical excitation into the experiment, free carriers can be excited in the materials and, likely, the MI transition will be influenced. Our research will be focused on the dynamical process of the way that electrons are excited and combined with holes and how the photon-generated electrons interact with Mn ions. The impurity states will also be investigated. (3) To explore the effect of the strain on the electroresistance (ER) and photocarrier injection. Films with different thicknesses will be made to study the strain effect. It has been known that lattice strain can greatly affect the Curie temperature and the phase transition. Recently we also found that the strain can greatly influence the ER effect induced by currents. It could be associated with the multi-phases coexistence in R1-xAxMnO3, though the physical mechanism has not fully understood yet. The optical excitation is likely to influence the MI transition and introduce some metastable states as well. Thus the effect of lattice strain on the optical process is of great interest.

List of Research Outputs

Bai Z., Wang Z.H., Li P.J., Qiu L., Zhang H. and Gao J., Specific heat characteristics near T_c and low temperature in MTG Y_0.8Ca_0.2Ba₂Cu₃O_y crystals, Superconductor Science and Technology. Bristol, IOP Publishing Limited, 2006, 19: 1034-1039.

Gao J. and Hu F., The abnormal electroresistance behavior observed in epitaxial La_0.8Ca_0.2MnO₃ thin films, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 555-558.

Hao J.H. and Gao J., Characterization of oxide thin films using optical techniques, Applied Surface Science. Amsterdam, Elsevier B.V., 2006, 253: 372-375.

Hao J.H., Luo Z. and Gao J., Effects of substrate on the dielectric and tunable properties of epitaxial SrTiO₃ thin films, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 114107: 1-5.

Hao J.H., Gao J. and Wong H.K., Laser molecular beam epitaxy growth and properties of SrTiO₃ thin films for microelectronic applications, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 559-562.

Kang L., Gao J., Xu H., Zhao S.Q., Chen H. and Wu P.H., Epitaxial Mg₂SiO₄ thin films with a spinel structure grown on Si substrates, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 297: 100-104.

Li P.J., Bai Z., Li W.C., Qiu L., Zhang H., Gao J. and Wang Z.H., Critical current density of MTG-YBa₂Cu_2.99Li_0.01O_y crystals, Physica C. Amsterdam, Elsevier B.V., 2006, 439: 73-77.

Luo Z. and Gao J., Rectifying characteristics and photovoltaic effect in heterojunctions of La_0.9Sr_0.1MnO₃/Nb-doped SrTiO₃, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 056104: 1-3.

Zhai Z.Y., Wu X.S., Jiang Z.S., Hao J.H., Gao J., Cai Y.F. and Pan Y.G., Strain distribution in epitaxial SrTiO₃ thin films, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 262902: 1-3.

Zhang H.D., Li M., An Y.K., Mai Z.H., Gao J., Hu F., Wang Y. and Jia C.J., Thickness dependence of microstructures in La_0.8Ca_0.2MnO₃ thin films, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 013911: 1-4.

Zhang W.Y., Gao J. and Wu X.S., Second Class Natural Science Award from the Chinese Education Ministry (shared with W.Y. Zhang and X.S. Wu from Nanjing University) 2007, 中华人民共和国教育部自然科学奖二等奖, 2007.

Researcher : Gong M

List of Research Outputs

Gong M., A study of surface growth mechanism by kinetic Monte-Carlo simulation. Hong Kong, The University of Hong Kong, 2006, 1-61.

Xie M.H., Gong M., Pang K.Y., Wu H.S. and Tong S.Y., Origin of triangular island shape and double-step bunching during GaN growth by molecular-beam epitaxy under excess Ga conditions, Physical Review B. New York, The American Physical Society, 2006, 74: 085314:1-6.

Researcher : Gu Q

List of Research Outputs

Gu Q., Ling F.C.C., Cheung C.K., Luo J., Chen X., Djurisic A., Brauer G., Anwand W., Skorupa W., Reuther H. and Ong H.C., Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment, In: S. Ashok, P. Kiesel, J. Chevallier, T. Ogino, Materials Research Society Spring Meeting 2007, 9-13 April 2007, San Francisco, Symposium F: Semiconductor Defect Engineering--Materials, Synthetic Structures, and Devices II. Materials Research Society, 2007, 994: F11-15.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Researcher : Hao J

Project Title:	Laser molecular beam epitaxy growth and characterization of SrTiO3 thin films for tunable YBa2Cu3Oy applications
Investigator(s):	Hao JH, Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	12/2004

Abstract:

To investigate SrTiO₃ thin films that exhibit enhanced dielectric properties suitable for tunable YBa₂Cu₃O_y (YBCO) applications with the specific aims of: (1) well-controlled epitaxial growth of STO thin films by laser molecular beam epitaxy (MBE); (2) establishment of the correlations between the deposition parameters of STO thin films, their structural characteristics, and dielectric properties. Realization of the fundamental mechanisms of dielectric properties in STO thin films; (3) evaluation of the feasibility of laser MBE grown YBCO/STO multilayers for tunable applications.

Project Title:	Dielectric properties in novel perovskite oxide thin films
Investigator(s):	Hao JH
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	12/2004

Abstract:

Objective of the research proposal: Design and synthesis of novel functional oxides with unusual and promising dielectric properties. Investigation of processing effects on the structural and dielectric properties of thin films. Searching and understanding of some possible new phenomena in novel perovskite oxide thin films. The key issue is to investigate how the preparation parameters of perovskite oxide thin film affect their dielectric properties. The key problem is interfacial effects between novel perovskite oxides and various substrates. In the proposed investigation, the growth of epitaxial thin film with full control will be carried out. Various structural, dielectric and optical characterizations will be employed.

Project Title:	Substrate and buffer layer engineering for epitaxial perovskite titanate thin films
Investigator(s):	Hao JH, Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2006

Abstract:

Project objectives: To investigate heteroepitaxial structures of perovskite titanates like strontium titanate thin films grown on various substrates and buffer layers with the specific aims of: 1) Design and development of suitable sets of buffer layers/substrates used to improve physical properties of perovskite titanate thin films. 2) Determining interface and strain effects on the structural and dielectric properties of various controlled heterostructures. 3.Identifying and understanding of some new phenomena such as the possible occurrence of strain-induced FE in perovskite titanate films.

Researcher : Hao JH

Project Title:	Laser molecular beam epitaxy growth and characterization of SrTiO3 thin films for tunable YBa2Cu3Oy applications
Investigator(s):	Hao JH, Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	12/2004

Abstract:

Project Title:	Dielectric properties in novel perovskite oxide thin films
Investigator(s):	Hao JH
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	12/2004

Abstract:

Project Title:	Substrate and buffer layer engineering for epitaxial perovskite titanate thin films
Investigator(s):	Hao JH, Gao J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2006

Abstract:

List of Research Outputs

Hao J.H. and Gao J., Characterization of oxide thin films using optical techniques, Applied Surface Science. Amsterdam, Elsevier B.V., 2006, 253: 372-375.

Hao J.H., Gao J. and Wong H.K., Laser molecular beam epitaxy growth and properties of SrTiO₃ thin films for microelectronic applications, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 559-562.

Researcher : Harko TC

Project Title:	Radiation processes in the electrosphere of bare strange stars
Investigator(s):	Harko TC
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2006
Completion Date:	12/2006

Abstract:

Strange stars, consisting of deconfined quark matter, are particularly difficult to be differentiated observationally from neutron stars. Both quark and neutron stars have very similar masses and radii. Their detection is further complicated by the very low photon emissivity of the quark matter, which is six orders of magnitude below the black body energy flux. A bare strange star has a very sharp boundary surface, which prevents energy loss through emitting thermal X-rays from the stellar surface due to the extremely high plasma frequency. The main objective of this project is to study some properties of bare strange stars, offering some unique features which could help in the observational identification of this type of compact objects. Some specific objectives for this project are as follows: (1) A hot bare strange star may be a powerful source of electron-positron pairs, which are created in the electrosphere and can flow away from the star. We shall consider in detail the effects of the finite extension and rapid decrease of the electric field on the electron-positron pair creation and how they affect the luminosity of the star. We shall consider the pair creation process in strong variable electric fields in terms of an effective barrier penetration problem. To study the process of tunneling through the forbidden region we shall use wave function techniques and a WKB type approximation of the penetration factor. (2) The increases in the electron density and electric field intensity lead to a strong modification of the electron-electron bremsstrahlung radiation properties of the electron gas. Due to the extremely high plasma frequency radiation emission from the inner parts of the electrosphere is suppressed. However, electron-electron bremsstrahlung radiation emission can take place in the outer parts of the electron layer and thus the electrosphere is a source of low frequency X-ray radiation, which may be observable by a distant observer. Because of its specific and unique spectrum, this radiation could become the main observational signature for a bare strange star. We will study in detail the emissivity and spectrum of the radiation emitted by the outer layers of the electron gas, by considering in detail the effects of the degeneracy of the gas. (3) In order to have a better understanding of the radiation emission from the electrosphere we shall consider in detail the radiation transport inside the electrosphere. The most important physical process taking place in the electrosphere is the scattering of photons by the free electrons. Depending on this scattering the emission of the electrosphere could have a blackbody spectrum at the star surface temperature or the re-absorption of the emitted radiation could be unimportant. We shall study the radiation transport in the electrosphere by using both analytical and numerical approaches. We shall consider the radiation transport equation with both relativistic and non-relativistic sources of opacity. References [1] E. Witten, Phys. Rev. D 30, 272 (1984) [2] C. Alcock, E. Farhi and A. Olinto, Astrophys. J. 310, 261 (1986) [3] Ch. Kettner, F. Weber, M. K. Weigel and N. K. Glendenning, Phys. Rev. D 51, 1440 (1995) [4] P. Haensel, J.L. Zdunik and R. Schaeffer, Astron. Astrophys. 160, 121 (1986) [5] T. Chmaj, P. Haensel and W. Slomi\'nski, Nuclear Physics B (Proc. Suppl.) 24, 40 (1991) [6] V. V. Usov, Phys. Rev. Lett. 80, 230 (1998) [7] K. S. Cheng and T. Harko, Phys. Rev. D 62, 3001 (2000) [8] T. Harko and K. S. Cheng, Astron. Astrophys. 385, 947 (2002) [9] K. S. Cheng and T. Harko, Astrophys. J. 596, 451 (2003) [10] T. Harko, K. S. Cheng and P. S. Tang, Astrophys. J. 608, 945 (2004) [11] V. V. Usov, T. Harko and K. S. Cheng, Astrophys. J. 620, 915 (2005) [12] T. Harko and K. S. Cheng, Astrophys. J. 622, 1033 (2005)

Project Title:	Astrophysical constraints on the multi-dimensional space-time models
Investigator(s):	Harko TC, Cheng KS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2006

Abstract:

(1) The main puprpose of the present investigation is to provide a systematic framework for the observational testing of brane world and other higher dimensional models in astrophysical settings. The first step of the project is to consider realistic galactic models in brane world theories. In the external galactic space-time the non-zero contribution of the Weyl tensor from the bulk (the dark radiation and the dark pressure) generates some gravitational effects we interprete as the "dark matter". An important test of the possible explanation of dark matter as a higher dimensional effect is the motion of particles in stable circular orbits around galaxies. We will investigate the effects of the dark radiation and pressure on the behavior of the tangential velocity of test particles moving around galaxies. (2)The study of light deflection by galaxies and the gravitational lensing could discriminate between the brane world and the standard dark matter models.In addition to this effect we will also consider the use of other astrophysical data like,e.g., the data of WMAP, gamma-ray bursts etc., to constrain the multi-dimensional space-time models. (3) One of the most important and surprising discoveries in cosmology in recent years is the realization that our universe is dominated by a mysterious dark energy, which leads to an accelerating expansion of the Universe. We will investigate the possibility that dark energy can be also related to the existence of the extra-dimensions. We will consider the suggestion that signals from early Universe may give some promising signatures of extra-dimensions.

Project Title:	Gravitational radiation from compact binary systems
Investigator(s):	Harko TC, Cheng KS
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2007

Abstract:

1. Gravitational radiation from accreting binary systems Since its discovery in 1975 by Hulse and Taylor, the binary pulsar PSR 1913+16, consisting of a pulsar orbiting around an unseen companion star, has proved to be a powerful testing ground for gravitational theories. The most important measurement realized by using this system was the observation of orbital decay, which is due to gravitational radiation. Another important measurement was the determination of the masses of the stellar components of the system, which provided the most precise limits on neutron star masses currently known. A third major observational effect was the relativistic geodetic precession of the pulsar spin axis, providing the opportunity of mapping the pulsar beam in the latitude direction and a chance to observe the ''magnetic'' aspects of the gravity. On the other hand from observational point of view it has been shown that accretion in binaries with low-mass companions can lead to an important increase in the mass of the star. The amounts of matter accreted by the 18 radio pulsars in these binary systems exceed 0.5 solar masses. If at the beginning of the accretion process the masses of neutron stars are of the order of 1.4 solar masses, this means that accretion can lead to a major change in the mass of the star in the binary system. We propose to study the effects of the time variation of the gravitational mass on the energy loss via gravitational radiation in accreting binary systems, consisting of two point masses evolving around each other on Keplerian orbits, under their mutual gravitational influence, and in the presence of mass exchange between the two stars. The variation in the mass of the components leads to a modification of the gravitational energy emission, which in principle could be observationally detected as a supplementary change in the decay of the orbital period of the components of the binary system. 2. Spin effects in inspiralling compact binaries Gravitational radiation drives compact binaries through an inspiral phase towards a final coalescence. For binaries with spin, mass quadrupole and magnetic dipole moments, various contributions add to this process, which is characterized by the rate of increase of the gravitational wave frequency and the accumulated number of gravitational wave cycles. We propose to study the contributions of the spin-orbital angular momentum, spin-spin and quadrupole-monopole interactions contributions to the gravitational wave frequency, by using the post-Newtonian approximations. In particular we will carefully consider the contributions due to the self-interaction of individual spins. As a result of the precession of spins the magnitude L of the orbital angular momentum in the system is not conserved. Therefore a proper characterization of the radial motion in a binary system is provided by the energy E and the angular average over the angular momentum. These results can be tested with the observations of the proper spin-spin contributions for the recently discovered J0737-3039 double pulsar system.

List of Research Outputs

Bertolami O., Böhmer C.G., Harko T.C. and Lobo S.N., Extra force in f(R) modified theories of gravity, Physical Review D. New York, The American Physical Society, 2007, 75: 104016:1-5.

Bohmer C.G. and Harko T.C., Bounds on the basic physical parameters for anisotropic compact general relativistic objects, Classical and Quantum Gravity. United Kingdom, IOP, 2006, 23: 6479-6491.

Böhmer C.G. and Harko T.C., Can dark matter be a Bose-Einstein condensate?, Journal of Cosmology and Astroparticle Physics. United Kingdom, IOP, 2007, 06: 025.

Böhmer C.G. and Harko T.C., Dark energy as a massive vector field, European Physical Journal C - Particles and Fields. Berlin/Heidelberg, Springer, 2007, 50: 423-429.

Böhmer C.G. and Harko T.C., Minimum mass-radius ratio for charged gravitational objects, General Relativity and Gravitation. Berlin/Heidelberg, Springer, 2007, 39: 757-775.

Cheng K.S. and Harko T.C., High energy emission from strange stars, The Seventh Pacific Rim Conference on Stellar Astrophysics. Astronomical Society of the Pacific, 2007, 362: 141-150.

Researcher : Hong K

List of Research Outputs

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesis of potassium tungstate micro-walls by thermal evaporation, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 295: 75-78.

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesizing tungsten oxide nanowires by a thermal evaporation method, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 173121: 1-3.

Hong K., Xie M.H. and Wu H.S., Tungsten oxide nanowires synthesized by a catalyst-free method at low temperature, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 4830-4833.

Hu R., Wu H.S. and Hong K., Growth of uniform tungsten oxide nanowires with small diameter via a two-step heating process, Journal of Crystal Growth . 2007, 306: 305.

Researcher : Hsu YF

List of Research Outputs

Djurisic A., Leung Y.H., Tam K.H., Hsu Y.F., Ding L., Ge W.K., Zhong Y.C., Wong K.S., Chan W.K., Tam H.L., Cheah K.W., Kwok W.M. and Phillips D.L., Defect emissions in ZnO nanostructures, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 095702: 1-8.

Hsu Y.F., Djurisic A. and Tam K.H., Morphology and optical properties of ZnO nanostructures grown under zinc and oxygen-rich conditions, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2007, 304: 47-52.

Researcher : Hu F

Project Title:	Resistance switching induced by electric current in epitaxial films of perovskite manganites
Investigator(s):	Hu F, Gao J
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	09/2005
Completion Date:	02/2007

Abstract:

Colossal magnetoresistance (CMR) effect in mixed-valent perovskite manganites has triggered intense scientific activity in recent years. Phase separation together with concomitant percolation behavior has been supposed to be the core of CMR effect. It has been suggested that the largest MR is associated with spatial inhomogeneity related to multiphase coexistence, which generically causes a sensitivity of physical properties to external perturbations, such as application of magnetic fields, pressure, current bias, or light illumination. The possibility of using a wide range of perturbations to influence the transport properties also increases their technological potential. An increasing interest has been recently attracted to the influence of electric field/current to the transport in CMR materials.[1-4] Significant change of electric resistance induced by static electric field has been demonstrated in La1-xCaxMnO3 using field effect configurations. The observed electroresistance (ER) and CMR effects are found remarkably complementary and strongly favoring a percolative phase separation picture.[1] It has been also observed that an applied current could lead to a transition from the electrically insulating charge-ordered (CO) state to a ferromagnetic (FM) metallic state, even for Y0.5Ca0.5MnO3 in which a large magnetic field ( 40 T) has no effect on the charge-ordered state.[2] Considering the strong effect of external perturbations on the balance of multiphase coexistence, it can be expected that a sufficiently large current flowing and the possible produced magnetic fields could thoroughly disturb the subtle balance of multiphase coexistence and then might induce a new equilibrium state of coexistence. In comparing with bulk samples, a current with a very high density could be easily applied to a micro-bridge of CMR thin films thus the influence of high current density on the multiphase coexistence state can be studied. Recently, we focused on the influence of electric field/current on the transport properties in films of mixed-valent manganites. Remarkable ER effect induced by electric current has been observed even in epitaxial thin films of La0.7Ca0.3MnO3 and La0.85Ba0.15MnO3.[3] Further studies revealed that a current with a high density can significantly affect the balance of multiphase coexistence and cause a series of changes of transport properties.[4] Very recently, we found that a switching from low to high resistive state could be introduced by applying a dc current over a threshold value in epitaxial films of perovskite manganites. Our repeated measurements indicate that the high resistive state appeared in some samples is much stable. Exposing the sample in air and room temperature could not cause any change of the transport properties. However, for some other samples, the induced high resistive state behaves unstable characteristics. Keeping the sample at a low temperature of 20 K, a relaxation to a higher resistive state takes place. Our preliminary analysis indicated that the different resistance switching behavior is related to the different phase-separation characteristic in different systems. The work on the resistance switching behavior is still rather limited. The rich variation of the switching behavior versus temperature, current, and magnetic field in different perovskite manganites remain to be explored. In this proposed research, we will perform a comprehensive study on the current-induced resistance switching in epitaxial films of various manganite perovskites with different phase-separation characteristic. Scientific issues to be addressed: 1. To widely study the resistance switching behavior induced by electric current in epitaxial thin films of various mixed-valent manganite oxides with electronic phase separation. The films with different phase separation characteristic can be prepared by adjusting the kind and content of R and A ions in the formula of R1-xAxMnO3 (where R and A are rare- and alkaline-earth ions, respectively). 2. To study the influence of the strain on the resistance switching behavior. Strain effect, due to substrate, influence the lattice stiffness, Jahn-Teller distortion, and consequently the electronic phase separation. The epitaxial thin films with different thickness can be prepared so as to study the strain effect on the coexistence of multiphases and the current-induced resistance switching. 3. To study the influence of electric field and magnetic field on the switched high resistive state in different systems. Try to understand the physics mechanism behind the current-induced resistance switching. References: [1] T. Wu, et al., Phys. Rev. Lett. 86 (2001) 5998. [2] C. N. R. Rao, et al., Phys. Rev. B 61 (2000) 594. [3] J. Gao, S.Q. Shen, T.K. Li, and J.R. Sun, Appl. Phys. Lett. 82 (2003) 4732. [4] F. X. Hu, J. Gao, Phys. Rev. B 69 (2004) 212413.

List of Research Outputs

Gao J. and Hu F., The abnormal electroresistance behavior observed in epitaxial La_0.8Ca_0.2MnO₃ thin films, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 555-558.

Zhang H.D., Li M., An Y.K., Mai Z.H., Gao J., Hu F., Wang Y. and Jia C.J., Thickness dependence of microstructures in La_0.8Ca_0.2MnO₃ thin films, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 013911: 1-4.

Researcher : Hu R

List of Research Outputs

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesis of potassium tungstate micro-walls by thermal evaporation, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 295: 75-78.

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesizing tungsten oxide nanowires by a thermal evaporation method, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 173121: 1-3.

Hu R., Wu H.S. and Hong K., Growth of uniform tungsten oxide nanowires with small diameter via a two-step heating process, Journal of Crystal Growth . 2007, 306: 305.

Researcher : Huang Y

List of Research Outputs

Huang Y., Lu Y., Wong Y.L. and Cheng K.S., A detailed study on the equal arrival time surface effect in gamma-ray burst afterglows, Chinese Journal of Astronomy and Astrophysics. National Natural Science Foundation of China, 2007, 7: 397-404.

Researcher : Hui CW

List of Research Outputs

Hui C.W., Positron annihilation spectroscopic studies of undoped N-type zinc oxide single crystal. Hong Kong, The University of Hong Kong, 2006, 1-68.

Hui C.W., Zhang J., Zhou T., Ling F.C.C., Beling C.D., Fung S.H.Y., Brauer G., Anwand W. and Skorupa W., Positron annihilation study of hydrothermal grown n-type zinc oxide, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Researcher : Jia J

List of Research Outputs

Becker W., Kramer M., Jessner A., Taam R.E., Jia J., Cheng K.S., Mignani R., Pellizzoni A., Luca A.D., Slowikowska A. and Caraveo P.A., A multiwavelength study of the pulsar PSR B1929+10 and its x-ray trail, The Astrophysical Journal. The American Astronomical Society, 2006, 645: 1421-1435.

Jia J. and Cheng K.S., Phase-resolved spectra of the crab pulsar, The Seventh Pacific Rim Conference on Stellar Astrophysics. Astronomical Society of the Pacific, 2007, 362: 97-104.

Researcher : Jia J

List of Research Outputs

Jia J. and Cheng K.S., Phase-resolved spectra of the crab pulsar, The Seventh Pacific Rim Conference on Stellar Astrophysics. Astronomical Society of the Pacific, 2007, 362: 97-104.

Researcher : Jin K

List of Research Outputs

Jin K. and Xu S.J., Fano resonance in the luminescence spectra of donor bound excitons in polar semiconductors, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 032107: 1-3.

Researcher : Kang L

List of Research Outputs

Kang L., Gao J., Xu H., Zhao S.Q., Chen H. and Wu P.H., Epitaxial Mg₂SiO₄ thin films with a spinel structure grown on Si substrates, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 297: 100-104.

Researcher : Lam CH

List of Research Outputs

Lam C.H. and Ling F.C.C., Decomposition of positron lifetime spectra generated by Monte Carlo method: The case study of 6H silicon carbide, Nuclear Instruments and Methods in Physics Research B. Amsterdam, Elsevier B.V., 2006, 251: 479-483.

Researcher : Leung CC

List of Research Outputs

Leung C.C. and Chau H.F., Weighted assortative and disassortative networks model, Physica A. Amsterdam, Elsevier B.V., 2007, 378: 591-602.

Researcher : Leung JKC

Project Title:	Muon-induced neutron background in Gd-doped liquid scintillator in an underground laboratory
Investigator(s):	Leung JKC, Pun JCS, Chu MC
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	02/2005
Completion Date:	01/2007

Abstract:

Purpose: To study the muon-induced neutron background in Gd-doped liquid scintillator in an underground laboratory inside Aberdeen Tunnel (Aberdeen Lab). Key issues and problems being addressed: Recent discoveries have shown that neutrinos are massive and that it can oscillate between 3 neutrino species (electron neutrino; muon neutrino and tau neutrino). Mixing among the flavours has been observed in atmospheric and solar neutrinos in experiments such as Super-K and SNO as well as in experiments using man-made neutrino sources including KamLAND and K2K. In the neutrino mixing matrix, all but two parameters have been measured: the smallest mixing angle, theta-13, and the value of the CP violating phase, are not yet known. In order to advance our knowledge in neutrino physics and indeed the nature of dark matters in the universe, a few collaborations in the world have been formed and started the race for determining theta-13. China with Hong Kong and US have formed a collaboration to measure the mixing angle using anti-neutrinos produced by the reactors of the Daya Bay and Ling Ao nuclear power plants. (Please refer to http://dayawane.ihep.ac.cn/ for details). We are convinced that the Daya Bay site is the best and most promising one because it is one of the largest reactor groups in the world and the mountain next to the site provides sufficient overburden for minimizing the cosmic background effects. Because of the small interaction cross-section of neutrinos, event rate at the neutrino detectors will be extremely small, hence suppression of background and false events are crucial to the success of the experiments. The reactor neutrino-oscillation experiments, CHOOZ, Palo Verde (Boehm et al, 2000) and the KamLAND (Alivisatos et al, 1998), have shown that muon-induced neutrons are serious background events. In this proposal we will investigate the production and the properties of the background neutrons produced inside a liquid scintillator of the same type that will be used in the future Daya Bay experiment. The experiment will be done inside the Aberdeen Lab which has an overburden of 250 m of rock and geology, close to that of the proposed near-detector sites in the Daya Bay neutrino project. We expect to obtain reliable data within about one and a half year, just good enough to be incorporated into the fabrication of the future Daya Bay detectors. References: Boehm, F., et al, Search for Neutrino Oscillations at the Palo Verde Nuclear Reactors. Phys. Rev. Lett, 84, 3764-3767, 2000. Alivisatos, P. et al., KamLAND: a Liquid Scintillator AntiNeutrino Detector at the Kamioka site. Report No. Stanford-HEP-98-03, Tohoku-RCNS-98-15, 1998.

Project Title:	Hong Kong radon map
Investigator(s):	Leung JKC, Jiao JJJ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2007

Abstract:

(1) The project is related to environmental radioactivity and it has the following objectives: - To produce a Hong Kong Radon Map (GIS) in the scale of approximately 1:100,000. - To evaluate and improve the 10-point system that correlates the Radon Map with outdoor radon concentration in the environment of Hong Kong. (2) Key issues and problems: - Radon and its progenies have been known to contribute on average about 50% of the natural radiation dose to the world population. In Hong Kong, the Principal Investigators (PI) have worked on the health hazard of radon for more than a decade and have shown that the average radiation dose due to radon received by people in Hong Kong is much higher than the world average and that the average gamma radiation dose is even the highest in the world, all are results of the high U-238 and Th-232 contents in local rocks. (3) Though many workers have measured radon in Hong Kong, there is not yet a complete map of the territory showing the soil radon potential, which is based on geological, topographical and structural elements. - The radon map will show the distribution of the soil radon potential or local radon risk to the public rather than just showing the ambient radon levels at the time of measurement. (4) The maps will provide valuable information of the local radon and radionuclide situation and will be useful databases for urban planning and building construction in terms of radiation protection to the workers as well as to the general public. - The maps will only cover the rural areas but not the built-up areas. - These kinds of work are practiced in western countries only in recent years. (5) A 10-point system was invented recently by the German co-investigator to correlate indoor radon concentration and soil radon potential with great success. - Because Hong Kong has a lot of coastal areas where the radon potential could be affected by the sea in addition to land topography, the 10-point system has to be modified and adapted to the environment of Hong Kong. (6) Deliverables - A GIS Hong Kong Radon Map in the scale of approximately 1:100,000. - A GIS map of distribution of soil radon concentrations, soil gas permeability and soil radionuclide contents. - A modified 10-point system for the environment of Hong Kong. (7) To establish the relation of indoor radon concentration in low-rises and lower floors of buildings with the radon potential.

List of Research Outputs

Leung S.Y.Y., Nikezic D., Leung J.K.C. and Yu K.N., A study of the polyethylene membrane used in diffusion chambers for radon gas concentration measurements, Nuclear Instruments and Methods in Physics Research B. Amsterdam, Elsevier B.V., 2007, 263: 311-316.

Leung S.Y.Y., Nikezic D., Leung J.K.C. and Yu K.N., Sensitivity of LR 115 SSNTD in a diffusion chamber, Nuclear Instruments and Methods in Physics Research B. Amsterdam, Elsevier B.V., 2007, 263: 306-310.

Yang D., Zhang J., Leung J.K.C., Beling C.D. and Liu L.B., Coincidence doppler broadening study in electron-irradiated polyurethane, Nuclear Instruments & Methods in Physics Research (Section B). Amsterdam, Elsevier B.V., 2007, 259: 933-936.

Zheng D., Leung J.K.C., Lee B.Y. and Lam H.Y., Data assimilation in the atmospheric dispersion model for nuclear accident assessments, Atmospheric Environment. Elsevier Ltd., 2007, 41: 2438-2446.

Researcher : Leung YH

List of Research Outputs

Chan S.W., Barille R., Nunzi J.M., Tam K.H., Leung Y.H., Chan W.K. and Djurisic A., Second harmonic generation in zinc oxide nanorods, Applied Physics B. Berlin, Springer-Verlag, 2006, 84: 351-355.

Djurisic A. and Leung Y.H., Optical properties of ZnO nanostructures, Small. Weinheim, WILEY-VCH Verlag GmbH & Co., 2006, 2: 944-961.

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Tse C.W., Leung Y.H., Tam K.H., Chan W.K. and Djurisic A., Tailoring and modifications of a ZnO nanostructure surface by the layer-by-layer deposition technique, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 3563-3568.

Researcher : Li D

List of Research Outputs

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Kwok W.M., Djurisic A., Leung Y.H., Li D., Tam K.H., Phillips D.L. and Chan W.K., Influence of annealing on stimulated emission in ZnO nanorods, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 183112: 1-3.

Researcher : Li G

List of Research Outputs

Li Q., Xu S.J., Li G., Dai D. and Che C.M., Two-photon photoluminescence and excitation spectra of InGaN/GaN quantum wells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 011104: 1-3.

Researcher : Li J

List of Research Outputs

Cui X., Shen S.Q., Li J., Ji Y., Ge W.K. and Zhang F.C., Observation of electric current induced by optically injected spin current, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 242115: 1-3.

Researcher : Li P

List of Research Outputs

Li P., Zhang G.M. and Shen S.Q., SU(3) bosons and the spin nematic state on the spin-1 bilinear-biquadratic triangular lattice, Physical Review B. New York, The American Physical Society, 2007, 75: 104420: 1-8.

Researcher : Li Q

List of Research Outputs

Li Q., Xu S.J., Li G., Dai D. and Che C.M., Two-photon photoluminescence and excitation spectra of InGaN/GaN quantum wells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 011104: 1-3.

Wei Z., Xu S.J. and Li Q., Spontaneous emission mechanisms of GaInAsN/GaAs quantum dot systems, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 124311:1-6.

Researcher : Li Y

List of Research Outputs

Li Y., Wang Z.D. and Sun C.P., Quantum criticality in a generalized Dicke model, Physical Review A. New York, The American Physical Society, 2006, 74: 023815:1-5.

Researcher : Ling FCC

Project Title:	Carbon vacancy defect and carbon interstitial defect in silicon carbide: unambiguous determination of their signature photoluminescence lines
Investigator(s):	Ling FCC
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2004
Completion Date:	10/2006

Abstract:

To measure the signature luminescence lines of the carbon vacancy and the carbon interstitial in the photoluminescence spectrum.

Project Title:	Experimental studies of defects in ZnO: electrical and optical activities of O-vacancy and Zn-vacancy related defects
Investigator(s):	Ling FCC, Xu SJ, Chen X
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	12/2004

Abstract:

To identify and characterize different defects in as-grown and particle irradiated ZnO. Annealing behaviors of the defects will also be investigated; to study the correlation between the identified defects and to investigate their microstructure; to study the involvement of O-vacancy and Zn-vacancy in PL transition; to study the role of O-vacancy and Zn-vacancy in determining the material electrical properties.

Project Title:	Natures and identities of defects in 6H silicon carbide induced by low energy electron irradiation
Investigator(s):	Ling FCC, Fung SHY
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	08/2005

Abstract:

To study the defects in low energy electron irradiated 6H-SiC with the use of positron annihilation spectroscopy, deep level transient spectroscopy, deep level optical spectroscopy and photoluminescence, while bearing the following objectives: (1) Characterize and identify the defects induced in low energy electron irradiated 6H-SiC material, as well as their annealing derivatives; (2) Explore the physical identities of the DLTS signals E1/E2, the PL signals D1 and EA; and (3) Study the role of these defects played in compensating the material, in particular for the case of carbon vacancy related defects.

Project Title:	Fabrication of good quality Schottky contact on n-ZnO materials
Investigator(s):	Ling FCC
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2007

Abstract:

Zinc oxide is a wide band gap semiconductor that has potential applications in fabricating optoelectronic devices operating in the UV wavelength, transparent high power electronic devices and piezo-electric transducers [1,2]. As compared to the other direct band gap wide bandgap semiconductor GaN that have already found various applications in optoelectronic devices, ZnO has the advantages of the availability of its form in bulk single crystal, and its larger exciton binding energy [1,2]. Metal-semiconductor rectifying contact (Schottky contact) is an important structure for constructing electronic devices. The electrical properties of the contact depends on a lot of factors, such as the work functions of the corresponding metal and semiconductor, surface contamination, the interfacial states that pin the Fermi level at the metal-semiconductor junction, electrical active defects, or the formation of new chemical phase at the metal-semiconductor junction. For the case of n-type ZnO, there is only very limited knowledge on fabricating reliable and good quality Schottky contact. As referring to the ideal Schottky model, the Schottky barrier height is given by $W_{M}-A_{S}$, where $W_{M}$ is the work function of the metal and $A_{S}$ is the electron affinity of the semiconductor, and thus metals having large values of work function (like Au, Ag and Pt) would be expected to yield contact with large Schottky barrier height. Although there were some reports of fabricating rectifying contacts by using the metals of Au [1-6], Ag [5,7] Pd [8] and Pt [9-11] from some research groups, fabricating good quality Schottky contact to n-type ZnO was difficult and not easily reproducible. Fabricating metal contact onto the substrate without surface pre-treatment usually yields ohmic contact. In all of the successful cases, surface pre-treatments were needed to yield good quality rectifying contacts. These surface treatments included ozone exposure, plasma exposure, hydrogen peroxide and sulfide pre-treatments. However, the reasons for such observations were poorly understood and controversial. It has been associated by different research groups to carbon and OH contaminations, deep level defects, morphology, Fermi level pinning and interfacial state formation. Au/n-ZnO contact was the one that has received the most extensive attention although the fabricated rectifying contact has been reported to be thermally unstable. Diverged values of Schottky barrier height and ideality factor have been reported to be in the range of 0.50-0.71 eV and 1.05-2.00 respectively. Pt was the other metal that has also received some attention for fabricating Schottky contact (with barrier height ranging from 0.50-0.61 eV and ideality factor ranging from 1.15-1.70) because of its high metal work function. The present proposal aims to fabricate a high quality and reproducible Schottky contact on n-type ZnO. [1] U. Ozgur, Ya. I. Ailvov, C. Liu, A. Teke, M. A. Reshchikov, S. Dogan, V. Avrutin, S. –J. Cho and H. Morkoç, J. Appl. Phys. 98, 041301 (2005). [2] S. J. Pearton, D. P. Norton, K. Ip, Y. W. Heo, T. Steiner, Progress in Materials Science 50, 293 (2005). [3] B. J. Coppa, R. F. Davis, R. J. Nemanich, Appl. Phys. Lett. 82, 400 (2003). [4] H. L. Mosbacker, Y. M. Strzhemechny, B. D. White, P. E. Smith, D. C. Look, D. C. Reynolds, C. W. Litton, L. J. Brillson, Appl. Phys. Lett. 87, 012102 (2005). [5] A. Y. Polyakov, N. B. Smirnov, E. A. Kozhuknova, V. I. Vdovin, K. Ip, Y. W. Heo, D. P. Norton, S. J. Pearton, Appl. Phys. Lett. 83, 1575 (2003). [6] D. C. Oh, J. J. Kim, H. Makino, T. Hanada, M. W. Cho, T. Yao, H. J. Ko, Appl. Phys. Lett. 86, 042110 (2005). [7] H. Sheng, S. Muthukumar, N. W. Emanetoglu, Y. Lu, Appl. Phys. Lett. 80, 2132 (2002). [8] H. von Wenckstern, E. M. Kaidashev, M. Lorenz, H. Hochmuth, G. Biehne, J. Lenzner, V. Gottschalch, R. Pickenhain, M. Grundmann, Appl. Phys. Lett. 84, 79 (2004). [9] S. –H. Kim, H. –K. Kim, T. –Y. Seong, Appl. Phys. Lett. 86, 112101 (2005). [10] S. –H. Kim, H. –K. Kim, T. –Y. Seong, Appl. Phys. Lett. 86, 022101 (2005). [11] K. Ip, B. P. Gila, A. H. Onstine, E. S. Lambers, Y. W. Heo, K. H. Baik, D. P. Norton, J. R. LaRoche, F. Ren, Appl. Phys. Lett. 84, 5133 (2004).

Project Title:	Ion implantation of zinc oxide material: dopant activation and defect characterization
Investigator(s):	Ling FCC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2007

Abstract:

(1) Most of the attempts to introduce doping into ZnO were done on deposition grown materials (i.e. MBE, CVD or PVD etc.). However, ion implantation doping technique of ZnO is still immature and required more attention. With the aim to introduce n-type and p-type doping, ion implantation in ZnO materials is proposed to be performed. (2) Al and/or Ga implantations are proposed to introduce the n-type doping into the material. For p-type doping, N ion will be the focus of studies. Co-doping with group III and V elements will also be attempted to achieve the p-type doping. Studies of activating the implanted dopants by annealing will be performed. (3) The deep level defects induced by the ion implantation process will be studied by deep level transient spectroscopy. Attention will also be paid to the annealing effect of these deep level defects. Temperature dependent Hall measurement will also be performed to investigate the shallow acceptor/donor states introduced. (4) Positron annihilation spectroscopic technique will be employed to study the open volume defects created by the ion implantation process.

List of Research Outputs

Chen X., Ling F.C.C., Djurisic A., Brauer G., Anwand W., Skorupa W. and Reuther H., Influence of hydrogen peroxide treatment on Au/n-ZnO contact, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Gu Q., Ling F.C.C., Cheung C.K., Luo J., Chen X., Djurisic A., Brauer G., Anwand W., Skorupa W., Reuther H. and Ong H.C., Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment, In: S. Ashok, P. Kiesel, J. Chevallier, T. Ogino, Materials Research Society Spring Meeting 2007, 9-13 April 2007, San Francisco, Symposium F: Semiconductor Defect Engineering--Materials, Synthetic Structures, and Devices II. Materials Research Society, 2007, 994: F11-15.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Hui C.W., Zhang J., Zhou T., Ling F.C.C., Beling C.D., Fung S.H.Y., Brauer G., Anwand W. and Skorupa W., Positron annihilation study of hydrothermal grown n-type zinc oxide, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Lam C.H. and Ling F.C.C., Decomposition of positron lifetime spectra generated by Monte Carlo method: The case study of 6H silicon carbide, Nuclear Instruments and Methods in Physics Research B. Amsterdam, Elsevier B.V., 2006, 251: 479-483.

Tam K.H., Cheung C.K., Leung Y.H., Djurisic A., Ling F.C.C., Beling C.D., Fung S.H.Y., Kwok W.M., Chan W.K., Phillips D.L., Ding L. and Ge W.K., Defects in ZnO nanorods prepared by a hydrothermal method, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 20865-20871.

Researcher : Liu Y

List of Research Outputs

Liu Y., Wang J., Xie M.H. and Wu H.S., Incommensurate metallic surfactant layer on top of InN film, Surface Review and Letters. World Scientific Pub., 2006, 13: 815-818.

Wang J., So W.K., Liu Y., Wu H.S., Xie M.H. and Tong S.Y., Observation of a (√3x√3)-R30^o reconstruction on GaN(0001) by RHEED and LEED, Surface Science. Amsterdam, Elsevier B.V., 2006, 600: L169-L174.

Researcher : Liu Z

List of Research Outputs

Tse C.W., Man K.K.Y., Cheng K.W., Mak S.K., Chan W.K., Yip C.T., Liu Z. and Djurisic A., Layer-by-layer deposition of rhenium-containing hyperbranched polymers and fabrication of photovoltaic cells, Chemistry-A European Journal. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 13: 328-335.

Researcher : Lo MK

List of Research Outputs

Lo M.K., Modelling and observations of the circumstellar ring system of supernova 1987A with the hubble space telescope. Hong Kong, The University of Hong Kong, 2006, 1-153.

Researcher : Lu L

List of Research Outputs

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Researcher : Lu Y

List of Research Outputs

Huang Y., Lu Y., Wong Y.L. and Cheng K.S., A detailed study on the equal arrival time surface effect in gamma-ray burst afterglows, Chinese Journal of Astronomy and Astrophysics. National Natural Science Foundation of China, 2007, 7: 397-404.

Researcher : Luo J

List of Research Outputs

Gu Q., Ling F.C.C., Cheung C.K., Luo J., Chen X., Djurisic A., Brauer G., Anwand W., Skorupa W., Reuther H. and Ong H.C., Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment, In: S. Ashok, P. Kiesel, J. Chevallier, T. Ogino, Materials Research Society Spring Meeting 2007, 9-13 April 2007, San Francisco, Symposium F: Semiconductor Defect Engineering--Materials, Synthetic Structures, and Devices II. Materials Research Society, 2007, 994: F11-15.

Researcher : Luo Z

List of Research Outputs

Hao J.H., Luo Z. and Gao J., Effects of substrate on the dielectric and tunable properties of epitaxial SrTiO₃ thin films, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 114107: 1-5.

Luo Z. and Gao J., Rectifying characteristics and photovoltaic effect in heterojunctions of La_0.9Sr_0.1MnO₃/Nb-doped SrTiO₃, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 056104: 1-3.

Researcher : MacKeown PK

List of Research Outputs

MacKeown P.K., William Doberck - double star astronomer, Journal of Astronomical History and Heritage. 2007, 10: 49-64.

Researcher : Nahid F

List of Research Outputs

Nahid F., Beling C.D. and Fung S.H.Y., Temperature dependence study of positronium formation in high density polyethylene by positron annihilation lifetime spectroscopy, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3751-3754.

Researcher : Ng MCA

List of Research Outputs

Chan C.P., Gao J., Yue T.M., Surya C., Ng M.C.A., Djurisic A., Liu P.C.K. and Li M., Study of laser-debonded GaN LEDs, IEEE Transactions on Electron Devices. IEEE, 2006, 53: 2266-2272.

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Gu Q., Ling F.C.C., Chen X., Cheung C.K., Ng M.C.A., Beling C.D., Fung S.H.Y., Djurisic A., Lu L., Brauer G. and Ong H.C., Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 122101: 1-3.

Lu A.W., Chan J., Rakić A.D., Ng M.C.A. and Djurisic A., Optimization of microcavity OLED by varying the thickness of multi-layered mirror, Optical and Quantum Electronics. Springer, 2006, 38: 1091-1099.

Ng K.Y., Muley A.A., Chan Y.F., Ng M.C.A., Djurisic A. and Ngan A.H.W., Highly facetted metallic zinc nanocrystals fabricated by thermal evaporation, Materials Letters. Amsterdam, Elsevier B.V., 2006, 60: 2423-2427.

Ng M.C.A., Organic nanostructures: Fabrication and characterization. Hong Kong, The University of Hong Kong, 2007, 1-75.

Tong W.Y., Djurisic A., Xie M.H., Ng M.C.A., Cheung K.Y., Chan W.K., Leung Y.H., Lin H.W. and Gwo S., Metal phthalocyanine nanoribbons and nanowires, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 17406-17413.

Tong W.Y., Djurisic A., Ng M.C.A. and Chan W.K., Synthesis and properties of copper phthalocyanine nanowires, Thin Solid Films. Amsterdam, Elsevier B.V., 2007, 515: 5270-5274.

Researcher : Ning J

List of Research Outputs

Ning J., Xu S.J., Shi S. and Xie M.H., Slow oscillations in the low-temperature optical reflectance spectra of ZnO: Surface space-charge effect, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 061109: 1-3.

Researcher : Pang KY

List of Research Outputs

Xie M.H., Gong M., Pang K.Y., Wu H.S. and Tong S.Y., Origin of triangular island shape and double-step bunching during GaN growth by molecular-beam epitaxy under excess Ga conditions, Physical Review B. New York, The American Physical Society, 2006, 74: 085314:1-6.

Researcher : Pun JCS

Project Title:	Understanding the nature of Supernova Remnant 1987A
Investigator(s):	Pun JCS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2003

Abstract:

To study the Supermove Remnant ( SNR 1987A) in detail to gain insight on the explosion mechanism of the progenitor star, final stages of stellar evolution, and interaction with the circumstellar environment; to study SNR1987A system in detail: the explosion debris, the circumstellar rings, and the interaction between delmis and ring.

Project Title:	Radio telescope for physics and astronomy teaching and research
Investigator(s):	Pun JCS
Department:	Physics
Source(s) of Funding:	Leung Kau Kui Research and Teaching Endowment Fund - Teaching Grants
Start Date:	05/2004

Abstract:

Establish the first radio astronomical telescope in Hong Kong, strengthening the leadership of HKU on astronomy education; provide students with an all-rounded training in astronomy education; lay the foundation of radio astronomy research in Hong Kong; strengthen the role of HKU as the leading public voice on issues related to astronomy.

Project Title:	Understanding the nature of supernova remnant 1987A
Investigator(s):	Pun JCS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2006

Abstract:

(1) Supernova 1987A (SN 1987A) is a once-in-a-lifetime event which has not only provided the best-observed death of a star, but also the first-observed birth of a supernova remnant (SNR) in real time. We propose to study the SNR 1987A in detail to understand the explosion mechanism of the progenitor star, the final stages of stellar evolution, and the transfer of materials and energy of the exploded star to the interstellar environment. (2) The main goal of this project is to use the data taken from the Hubble Space Telescope (HST) to understand the nature of the various physical components of SN 1987A, including the inner explosion debris, the circumstellar gas system, and the interaction underway between the two. The high spatial resolution of the HST data allows the different components to be resolved and can thus be studied in detail separately. (3) We plan to study the evolution of the SN 1987A debris, important for understanding the dynamics and nature of the explosion itself. HST allows for the first time a young supernova explosion debris to be resolved and we hope to study its detailed structure. In addition, we hope to monitor the photometry energy output in the hope of providing a better limit of the energy output of the central compact object left behind from the supernova explosion, thus constraining its nature (e.g. is there a surviving companion, neutron star, or pulsar?). (4) One of the most exciting mysteries of SN 1987A is the circumstellar three-ring system. The rings are gas ejected by the progenitor star during the last phase of stellar evolution. They were ionized by the supernova shock breakout and have been recombining since. In addition to studying the bright equatorial inner ring, we propose to investigate the physical structure from the outer rings, which are only entirely resolved in the HST data. The results may provide insights to the mass loss history of the progenitor in the final stage of its evolution, from which the nature of the progenitor star can be deduced. (5) A recent development of the SN 1987A system is the detection of shock interaction between the fastest moving materials of the debris and the circumstellar gas, thus becoming a supernova remnant (SNR). SNR 1987A provides the first opportunity for this process to be monitored in real time and we plan to study the emission from the shock interaction. HST observations are useful for studying the temporal evolution of the various components of the interaction in detail. Combining with observations in other wavelengths, in particular radio and X-ray, we hope to come up with a more coherent picture of the physics involved. The results may shed light on processes such as induced stellar formations and the chemical enrichment of the universe.

Project Title:	Simulations of Particle Background and Design of Neutrino Detectors in Underground Laboratories
Investigator(s):	Pun JCS, Leung JKC
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	01/2007

Abstract:

Key objectives: 1. To use parameters and measurements from the Aberdeen Tunnel experiment to assist with the design of the Daya Bay experiment. 2. To perform simulations on all aspects of the Daya Bay experiment, in particular the calculations of experimental background due to the cosmic-ray and natural radioactivity of experimental components. Recent discoveries have shown that neutrinos are massive and that it can oscillate between three neutrino species, providing the first definitive evidence requiring extension of the Standard Model of particle physics. With previous solar, atmospheric, reactor, and accelerator experiments, we have found that neutrino masses are very small and have measured the two large mixing angles theta-12 and theta-23. However, only an upper limit was available for the remaining parameter theta-13. A group of scientists, from China, Hong Kong, Taiwan, the US, and a few other countries have formed a collaboration to carry out the Daya Bay Reactor Neutrino Experiment (referred here as the Daya Bay Experiment), with a goal of measuring sin^2(theta-13) to a sensitivity of 0.01. The underground laboratory in the Aberdeen Tunnel of Hong Kong (referred as the Aberdeen Laboratory) is serving as a satellite laboratory for doing R&D for the Daya Bay Experiment which is scheduled to commence in 2008. With the very tiny interaction cross-section of low-energy neutrinos, event rate at the neutrino detectors is expected to be extremely small. Therefore suppression of background events is crucial to the success of the Daya Bay Experiment. One of the most important sources of background in underground laboratories is the muon-induced neutrons. In a earlier Seed Funding proposal submitted by Co-Investigator Leung, we have proposed the construction of a neutron detector to be installed inside the Aberdeen Laboratory to measure this important background. An application has been submitted in 2006 for the 2007-08 RGC Earmarked Grant exercise based on the initial results obtained from the Seed Funding. In this application, we propose to perform simulations using the results obtained from the Aberdeen Tunnel experiment to assist with the design and developments of the Daya Bay experiment. The rate of the background would have significant impact on the execution of the experiments, including the calirbation and data analysis procedures. We propose to simulate all aspects of the experiment with this knowledge. In the Daya Bay experiment, neutrinos from the reactor cores are measured using a Gd-loaded liquid scintillator. The scintillator is housed in a transparent acrylic detector within a stainless steel tank. The weak signals from the scintillating photons will be detected by Photomultiplier Tubes (PMTs). The rate of neutrinos from various distances from the cores are measured to determine the disappearance rate of neutrinos owing to neutrino mixing. For this proposal, we will use simulation to optimize the design parameters for the various components of the neutron detector, including the geometry and size of the acrylic and steel detector vessels, the composition of the Gd-loaded liquid scintillator, and the layout of the photomultiplier tubes (PMTs) around the detector. Moreover, we propose to understand the experimental background of our detector (mostly from radioactive elements in the surrounding rocks and the equipments) and use the results to help to design the configuration and thickness of the shielding materials required for the experiment. Finally, we propose to simulate the efficiency of the calibration system, using both radioactive source and LED, to be deployed inside the Aberdeen Tunnel neutron detector. The result will be important both for verifying the accuracy of the simulation softwares and for providing key guidelines during this important design stage of the Daya Bay experiment. However, in addition to benefiting the Daya Bay experiment, it is worth pointing out that the knowledge of background radiation is essential to many other neutrino experiments carried out in underground environment, including dark matter and double beta-decay experiments.

List of Research Outputs

Researcher : Qiao Z

List of Research Outputs

Qiao Z., Ren W., Wang J. and Guo H., Low-field phase diagram of the spin Hall effect in the mesoscopic regime, Physical Review Letters. New York, The American Physical Society, 2007, 98: 196402: 1-4.

Ren W., Qiao Z., Wang J., Sun Q.F. and Guo H., Universal spin-Hall conductance fluctuations in two dimensions, Physical Review Letters. New York, The American Physical Society, 2006, 97: 066603: 1-4.

Researcher : Ren W

List of Research Outputs

Qiao Z., Ren W., Wang J. and Guo H., Low-field phase diagram of the spin Hall effect in the mesoscopic regime, Physical Review Letters. New York, The American Physical Society, 2007, 98: 196402: 1-4.

Ren W., Charge and spin conductance fluctuation and distribution in electronic transport. Hong Kong, The University of Hong Kong, 2006, 1-95.

Ren W., Wang J., Ma Z.S. and Guo H., Dynamical conductance of model DNA sequences, The Journal of Chemical Physics. New York, American Institute of Physics, 2006, 125: 164704: 1-5.

Ren W., Reimers J.R., Hush N.S., Zhu Y., Wang J. and Guo H., Models for the structure and electronic transmission of carbon nanotubes covalently linked by a molecular bridge via amide couplings, The Journal of Physical Chemistry C. American Chemical Society, 2007, 111: 3700-3704.

Ren W., Qiao Z., Wang J., Sun Q.F. and Guo H., Universal spin-Hall conductance fluctuations in two dimensions, Physical Review Letters. New York, The American Physical Society, 2006, 97: 066603: 1-4.

Wang B., Zhu Y., Ren W., Wang J. and Guo H., Spin-dependent transport in Fe-doped carbon nanotubes, Physical Review B. New York, The American Physical Society, 2007, 75: 235415:1-7.

Wang J., Wang B.G., Ren W. and Guo H., Conservation of spin current: Model including self-consistent spin-spin interaction, Physical Review B. New York, The American Physical Society, 2006, 74: 155307:1-5.

Researcher : Rice TM

List of Research Outputs

Chen Y., Rice T.M. and Zhang F.C., Atomic scale rotational symmetry breaking in lightly doped Ca_2-xNa_xCuO₂Cl₂, Physica C. Amsterdam, Elsevier B.V., 2007, 460-462: 234-237.

Chen Y., Rice T.M. and Zhang F.C., Rotational symmetry breaking in the ground state of sodium-doped cuprate superconductors, Physical Review Letters. New York, The American Physical Society, 2006, 97: 237004: 1-4.

Researcher : Shangguan M

List of Research Outputs

Shangguan M. and Wang J., Shot noise of charge current and spin current in the presence of Rashba interaction, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 145401: 1-8.

Researcher : Shao L

List of Research Outputs

Shao L., Wang Z.D. and Xing D.Y., Implementation of quantum gates based on geometric phases accumulated in the eigenstates of periodic invariant operators, Physical Review A (Brief Reports). New York, The American Physical Society, 2007, 75: 014301: 1-4.

Researcher : Shen R

List of Research Outputs

Shen R., Chen Y., Wang Z.D. and Xing D.Y., Conservation of spin currents in spin-orbit-coupled systems, Physical Review B. New York, The American Physical Society, 2006, 74: 125313:1-5.

Researcher : Shen S

Project Title:	Decoherence and non-exponential relaxation of quantum tunnelling in nano-magnetic molecules
Investigator(s):	Shen SQ, Chen Z
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2002

Abstract:

To understand the physical mechanism of decoherence and non-exponential relaxation in quantum tunnelling in nano-magnetic molecules.

Project Title:	Local stray field and macroscopic quantum tunneling in nanometer-sized magnetic particles and clusters
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2003

Abstract:

To understand the role of environmental interaction in quantum tunneling and decoherence from the magnetization reversal in nanometer-sized clusters, to establish an efficient method to deduce microscopic parameters from the experimental data, to study the novel properties of newly synthesized supramolecular dimers, and to explore possible application in magnetic memory and information industry.

Project Title:	Quantum spin transport and geometric phases
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003

Abstract:

To understand the relation between quantum spin transport and geometric phases in some mesocopic structures where spin and charge currents could arise from the spin interference.

Project Title:	Exact real space renormalization group transformation and its application to the spin and electron lattice systems
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2004

Abstract:

To develop a non-perturbative theory for the spin and electron lattices in strongly correlated electron systems.

Project Title:	Generation and coherent control of spin current in metals and semiconductors
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2004

Abstract:

To investigate spin transport in metals and semiconductors, and to explore possible measurement of pure spin current.

Project Title:	Spin coherent transport of electrons in metals and semiconductors
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2005

Abstract:

The primary objective of this proposal is to investigate spin coherent transport of electrons, especially how to generate and control spin current of electrons in metals and semiconductors.

Project Title:	Spin transverse force and its applications in quantum spin and charge transport
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2006

Abstract:

(1) Purpose: The primary objective of this proposal is to investigate the motion of electron spins in an electric field and in electronic systems with strong spin-orbit coupling. This project will focus on the electron transport driven by the spin polarized current and spin current, and spin dependent effects such as the Aharonov-Casher effect and its relevance to spin transport. (2) Key issues: Spin-orbit coupling reflects the interaction of the electron spin, electron momentum and its environments. It is a potential route to control and to manipulate quantum spin state and coherent transport. As an extension of Ehrenfest’s theorem a quantum mechanical version of spin transverse force can be obtained in electronic systems with strong spin-orbit coupling. This force and the force balance in equilibrium states are very useful to investigate the spin transport effect. Based on the concept of spin force it will be anticipated to develop a theory for spin resolved charge quantum transport driven by spin polarized current and spin current, and anomalous charge transport in ferromagnetic metals and semiconductors, and to establish a relation between spin current and spin polarization. (3) Likely outcome: It is expected to develop a quantum transport theory based on the extended Ehrenfest’s theorem on spin force. The research results will be reported in the leading physics journals, such as Physical Review and Physics Review Letters.

List of Research Outputs

Researcher : Shen SQ

Project Title:	Decoherence and non-exponential relaxation of quantum tunnelling in nano-magnetic molecules
Investigator(s):	Shen SQ, Chen Z
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2002

Abstract:

To understand the physical mechanism of decoherence and non-exponential relaxation in quantum tunnelling in nano-magnetic molecules.

Project Title:	Local stray field and macroscopic quantum tunneling in nanometer-sized magnetic particles and clusters
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2003

Abstract:

Project Title:	Quantum spin transport and geometric phases
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003

Abstract:

To understand the relation between quantum spin transport and geometric phases in some mesocopic structures where spin and charge currents could arise from the spin interference.

Project Title:	Exact real space renormalization group transformation and its application to the spin and electron lattice systems
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2004

Abstract:

To develop a non-perturbative theory for the spin and electron lattices in strongly correlated electron systems.

Project Title:	Generation and coherent control of spin current in metals and semiconductors
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2004

Abstract:

To investigate spin transport in metals and semiconductors, and to explore possible measurement of pure spin current.

Project Title:	Spin coherent transport of electrons in metals and semiconductors
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2005

Abstract:

The primary objective of this proposal is to investigate spin coherent transport of electrons, especially how to generate and control spin current of electrons in metals and semiconductors.

Project Title:	Spin transverse force and its applications in quantum spin and charge transport
Investigator(s):	Shen SQ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2006

Abstract:

List of Research Outputs

Cui X., Shen S.Q., Li J., Ji Y., Ge W.K. and Zhang F.C., Observation of electric current induced by optically injected spin current, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 242115: 1-3.

Li P., Zhang G.M. and Shen S.Q., SU(3) bosons and the spin nematic state on the spin-1 bilinear-biquadratic triangular lattice, Physical Review B. New York, The American Physical Society, 2007, 75: 104420: 1-8.

Shen S.Q., Invited Talk: Electric Current induced by Optically Injected Spin Current -- Theoretical Study and Experimental Consequence, Workshop on Mesoscopic and Spin Physics 2007. 2007.

Shen S.Q., Invited talk: Topological quantum phase transition and the Berry phase near the Fermi surface, The 1st International Symposium on Quantum Manipulation of Photons and Atoms, Beijing, China . 2007.

Yao Y.G., Liang Y.C., Xiao D., Niu Q., Shen S.Q., Dai X. and Fang Z., Theoretical evidence of the Berry-phase mechanism in anomalous Hall transport: First-principles studies of CuCr₂Se₄₋_xBr_x, Physical Review B (Rapid Communications). New York, The American Physical Society, 2007, 75: 020401: 1-4.

Zhou B. and Shen S.Q., Deduction of pure spin current from the linear and circular spin photogalvanic effect in semiconductor quantum wells, Physical Review B. New York, The American Physical Society, 2007, 75: 045339: 1-6.

Researcher : Shi M

List of Research Outputs

Shi M., Xie M.H., Wu H.S., Wang N. and Tong S.Y., Transition between wurtzite and zinc-blende GaN: An effect of deposition condition of molecular-beam epitaxy, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 151921:1-3.

Researcher : Shi S

List of Research Outputs

Dai D., Xu S.J., Shi S., Xie M.H. and Che C.M., Observation of both second-harmonic and multiphoton-absorption-induced luminescence in ZnO, IEEE Photonics Technology Letters. IEEE, 2006, 18: 1533-1535.

Li J., Shi S., Wang Y., Xu S.J., Zhao D.G., Zhu J.J., Yang H. and Lu F., Violet electroluminescence of AlInGaN-InGaN multiquantum-well light-emitting diodes: Quantum-confined stark effect and heating effect, IEEE Photonics Technology Letters. IEEE, 2007, 19: 789-791.

Lui T.Y., Zapien J.A., Tang H., Ma D.D.D., Liu Y.K., Lee C.S., Lee S.T., Shi S. and Xu S.J., Photoluminescence and photoconductivity properties of copper-doped Cd_1-xZn_xS nanoribbons, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 5935-5940.

Ning J., Xu S.J., Shi S. and Xie M.H., Slow oscillations in the low-temperature optical reflectance spectra of ZnO: Surface space-charge effect, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 061109: 1-3.

Wang R., Xu S.J., Shi S., Beling C.D., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au/GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 143505: 1-3.

Researcher : So WK

List of Research Outputs

So W.K., A study of surface properties of III-nitride semiconductors by first principle total energy calculation. Hong Kong, The University of Hong Kong, 2006, 1-61.

Wang J., So W.K., Liu Y., Wu H.S., Xie M.H. and Tong S.Y., Observation of a (√3x√3)-R30^o reconstruction on GaN(0001) by RHEED and LEED, Surface Science. Amsterdam, Elsevier B.V., 2006, 600: L169-L174.

Researcher : So WK

List of Research Outputs

So W.K., A study of surface properties of III-nitride semiconductors by first principle total energy calculation. Hong Kong, The University of Hong Kong, 2006, 1-61.

Researcher : Suen WM

List of Research Outputs

Jin K.J. and Suen W.M., Critical phenomena in head-on collisions of neutron stars, Physical Review Letters. New York, The American Physical Society, 2007, 98: 131101: 1-4.

Researcher : Tam KH

List of Research Outputs

Brauer G., Anwand W., Grambole D., Skorupa W., Hou Y., Andreev A., Teichert C., Tam K.H. and Djurisic A., Non-destructive characterization of vertical ZnO nanowire arrays by slow positron implantation spectroscopy, atomic force microscopy, and nuclear reaction analysis, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 195301: 1-8.

Chan S.W., Barille R., Nunzi J.M., Tam K.H., Leung Y.H., Chan W.K. and Djurisic A., Second harmonic generation in zinc oxide nanorods, Applied Physics B. Berlin, Springer-Verlag, 2006, 84: 351-355.

Djurisic A., Leung Y.H., Tam K.H., Hsu Y.F., Ding L., Ge W.K., Zhong Y.C., Wong K.S., Chan W.K., Tam H.L., Cheah K.W., Kwok W.M. and Phillips D.L., Defect emissions in ZnO nanostructures, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 095702: 1-8.

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Hsu Y.F., Djurisic A. and Tam K.H., Morphology and optical properties of ZnO nanostructures grown under zinc and oxygen-rich conditions, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2007, 304: 47-52.

Kwok W.M., Djurisic A., Leung Y.H., Li D., Tam K.H., Phillips D.L. and Chan W.K., Influence of annealing on stimulated emission in ZnO nanorods, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 183112: 1-3.

Tam K.H., Cheung C.K., Leung Y.H., Djurisic A., Ling F.C.C., Beling C.D., Fung S.H.Y., Kwok W.M., Chan W.K., Phillips D.L., Ding L. and Ge W.K., Defects in ZnO nanorods prepared by a hydrothermal method, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 20865-20871.

Tse C.W., Leung Y.H., Tam K.H., Chan W.K. and Djurisic A., Tailoring and modifications of a ZnO nanostructure surface by the layer-by-layer deposition technique, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 3563-3568.

Researcher : Teo CYJ

List of Research Outputs

Teo C.Y.J., Geometric phase and spin transport in quantum systems. Hong Kong, The University of Hong Kong, 2007, 1-141.

Researcher : Tong WY

List of Research Outputs

Tong W.Y., Djurisic A., Xie M.H., Ng M.C.A., Cheung K.Y., Chan W.K., Leung Y.H., Lin H.W. and Gwo S., Metal phthalocyanine nanoribbons and nanowires, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 17406-17413.

Tong W.Y., Organic optoelectronic materials: optical properties and 1D nanostructure fabrication. Hong Kong, The University of Hong Kong, 2006, 1-107.

Tong W.Y., Djurisic A., Ng M.C.A. and Chan W.K., Synthesis and properties of copper phthalocyanine nanowires, Thin Solid Films. Amsterdam, Elsevier B.V., 2007, 515: 5270-5274.

Researcher : Wang B

List of Research Outputs

Wang B., Zhu Y., Ren W., Wang J. and Guo H., Spin-dependent transport in Fe-doped carbon nanotubes, Physical Review B. New York, The American Physical Society, 2007, 75: 235415:1-7.

Researcher : Wang H

List of Research Outputs

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Wang H., Block copolymer thin films for nanometer pattern generation and nanostructure synthesis. Hong Kong, The University of Hong Kong, 2006, 1-138.

Wang H., Yip C.T., Cheung K.Y., Djurisic A., Xie M.H., Leung Y.H. and Chan W.K., Titania-nanotube-array-based photovoltaic cells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 023508: 1-3.

Researcher : Wang J

Project Title:	First principle calculation of transport properties of hybrid superconducting nanostructures
Investigator(s):	Wang J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2003

Abstract:

To study DC transport through hybrid superconducting nanostructures; to study AC cument through hybrid superconducting nanostructures; to study the shot noise of hybrid superconducting nanostructures.

Project Title:	Parametric pumping in nanostructures
Investigator(s):	Wang J
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003
Completion Date:	09/2006

Abstract:

To extend the previous parametric electron pumping theory to include the spin polarized pumping effect, and to examine the spin valve effect for the pumped current.

Project Title:	The noise spectrum of spin current
Investigator(s):	Wang J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004

Abstract:

To focus on the shot noise of the spin cument generated by various parametric quantum spin pumps such as these pumps with or without the spin flipping mechanism, with or without strong electron and electron interaction; to explore novel ways of generating spin cument in orderto study the correlation of the spin current.

Project Title:	Spin current in nanostructures
Investigator(s):	Wang J
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2004
Completion Date:	09/2006

Abstract:

To examine the possibility of SFET operation without involving magnetic materials and to exploit such a novel SFET which operates purely on spin current.

Project Title:	Time dependent transport through molecular devices
Investigator(s):	Wang J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	12/2005

Abstract:

The objective of this project is to study the time-dependent current driven by two kinds of ac bias: periodic field and pulse-like aperiodic field, from which one can obtain the information of the response time as well as the dynamical nature of the system. In order to achieve this, one has to solve a general time-dependent transport problem using Keldysh non-equilibrium Green’s function approach combined with the density function theory.

Project Title:	Quantum spin transport through nano-devices in the presence of spin-spin interaction
Investigator(s):	Wang J
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2006

Abstract:

(1) Recently, considerable interest has been paid to the quantum physics of spin-current. It is believed that a controlled spin-current generation, detection, and usage can provide interesting applications to spintronics. Spin-current generation has been classified as "extrinsic" or "intrinsic". An extrinsic spin-current is generated by external physical factors and driving forces of the spintronics device, such as optical spin injection achieved experimentally and the various spin pumps studied theoretically. An intrinsic spin-current is generated by physical factors existed inside the spintronic device, notable is that generated by various spin-orbit interactions. In particular, it has been theoretically predicted that non-magnetic systems with spin-orbit interaction and under an external electric field, can generate a spin-current flowing perpendicular to the electric field. Such an spin-current is termed "dissipation-less" because the electron motion is perpendicular to the electric field. (2) There are so far extensive theoretical work on spin-current physics, and some experimental works have also appeared which may provide support to some of the theories. Despite the increasing literature on spin-current physics, it is recognized that the definition of spin-current itself is still somewhat controversial. If one mimics the definition of charge-current, then a spin-current can be defined as the quantum average of the time derivative of spin density. In its simplest form at steady state, such a definition gives a spin-current that is equal to the particle current with spin-up subtracted by the particle current with spin-down multiplied by the spin of the electron. Clearly, this is a very intuitive definition of spin-current and is adopted by most of the work in literature. (3) Since both spin and velocity are vectors, the spin-current is a tensor. In systems where there is a spin-orbit interaction, the spin density is not conserved: spins can rotate from their initial orientation due to the interaction. Therefore, spin-current becomes a non-conservative quantity. A quantity which is not conserved is difficulty to study experimentally and indeed, it is unclear what is even measured if an experimental detection method can be found to measure spin-current. Without knowing what is measured, the definition of spin-current becomes non-unique and there have been several definitions in literature. Although it is unclear a priori if a measurable spin-current must be conserved, the property of conservation would be nice to have, at least theoretically. (4) In this project, we will investigate this problem by using the conventional definition of spin-current, but we will include a spin-spin interaction (bascally it is similar to the dipole-dipole interaction) into the Hamiltonian for computing the quantum average. Our preliminary result shows that the spin current obtained in such an analysis is conserved because the spin-spin interaction will generate a new term in the spin current which cancels the non-conserved spin current. Since dipole interactions between spins are possible, including their contribution and consequence of spin-current conservation in such a self-consistent analysis is rather natural. (5) In addition, the conserved spin-current gives a linear spin-conductance, we will develop a phenomenological theory for this spin-conductance for multi-probe device systems so that the spin-conductance is a conserved quantity. In this approach, we will enforce two conditions on the spin current: (1). the spin current must be conserved and (2). the spin current is caused by the external bias and hence depends only on the difference between external bias. With these two conditions, the non-conserved spin current can be partitioned into each electrode similar to the approach of Buttiker in treating ac charge transport. (6) Finally, with this new defintion of spin current developed and new spin-spin interaction introduced, the study of various spin transport properties can be carried on. For instance, we can examine the spin accumulation for a two-terminal device and spin Hall current for a four-terminal device with or without disorder as well as external magnetic field.

List of Research Outputs

Li C.S., Yu Y.J., Wei Y.D. and Wang J., Nonadiabatic quantum spin pump: Interplay between spatial interference and photon-assisted tunneling in two-dimensional Rashba systems, Physical Review B. New York, The American Physical Society, 2007, 75: 035312:1-8.

Liu Y., Wang J., Xie M.H. and Wu H.S., Incommensurate metallic surfactant layer on top of InN film, Surface Review and Letters. World Scientific Pub., 2006, 13: 815-818.

Maciejko J., Wang J. and Guo H., Time-dependent quantum transport far from equilibrium: An exact nonlinear response theory, Physical Review B. New York, The American Physical Society, 2006, 74: 085324:1-23.

Qiao Z., Ren W., Wang J. and Guo H., Low-field phase diagram of the spin Hall effect in the mesoscopic regime, Physical Review Letters. New York, The American Physical Society, 2007, 98: 196402: 1-4.

Ren W., Wang J., Ma Z.S. and Guo H., Dynamical conductance of model DNA sequences, The Journal of Chemical Physics. New York, American Institute of Physics, 2006, 125: 164704: 1-5.

Ren W., Reimers J.R., Hush N.S., Zhu Y., Wang J. and Guo H., Models for the structure and electronic transmission of carbon nanotubes covalently linked by a molecular bridge via amide couplings, The Journal of Physical Chemistry C. American Chemical Society, 2007, 111: 3700-3704.

Ren W., Qiao Z., Wang J., Sun Q.F. and Guo H., Universal spin-Hall conductance fluctuations in two dimensions, Physical Review Letters. New York, The American Physical Society, 2006, 97: 066603: 1-4.

Shangguan M. and Wang J., Shot noise of charge current and spin current in the presence of Rashba interaction, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 145401: 1-8.

Sun Q.F., Xie X.C. and Wang J., Persistent spin current in a mesoscopic hybrid ring with spin-orbit coupling, Physical Review Letters. New York, The American Physical Society, 2007, 98: 196801: 1-4.

Wang B., Zhu Y., Ren W., Wang J. and Guo H., Spin-dependent transport in Fe-doped carbon nanotubes, Physical Review B. New York, The American Physical Society, 2007, 75: 235415:1-7.

Wang J., Wang B.G., Ren W. and Guo H., Conservation of spin current: Model including self-consistent spin-spin interaction, Physical Review B. New York, The American Physical Society, 2006, 74: 155307:1-5.

Wang J., So W.K., Liu Y., Wu H.S., Xie M.H. and Tong S.Y., Observation of a (√3x√3)-R30^o reconstruction on GaN(0001) by RHEED and LEED, Surface Science. Amsterdam, Elsevier B.V., 2006, 600: L169-L174.

Wang J., Wang B.G. and Guo H., Quantum inductance and negative electrochemical capacitance at finite frequency in a two-plate quantum capacitor, Physical Review B. New York, The American Physical Society, 2007, 75: 155336:1-5.

Wu H., Xu S.J. and Wang J., Impact of the cap layer on the electronic structures and optical properties of self-assembled InAs/GaAs quantum dots, Physical Review B. New York, The American Physical Society, 2006, 74: 205329:1-6.

Xing Y.X., Sun Q.F. and Wang J., Symmetry and transport property of spin current induced spin-Hall effect, Phys. Rev. B. 2007, 75: 075324.

Xing Y.X., Sun Q.F. and Wang J., Symmetry and transport property of spin current induced spin-Hall effect, Physical Review B. New York, The American Physical Society, 2007, 75: 075324:1-7.

Zhao H. and Wang J., Photon-assisted shot noise in the mesoscopic system with a toroidal carbon nanotube coupled to normal-metal leads perturbed by ac fields, Physical Review B. New York, The American Physical Society, 2006, 74: 245401:1-11.

Researcher : Wang J

List of Research Outputs

Liu Y., Wang J., Xie M.H. and Wu H.S., Incommensurate metallic surfactant layer on top of InN film, Surface Review and Letters. World Scientific Pub., 2006, 13: 815-818.

Ren W., Wang J., Ma Z.S. and Guo H., Dynamical conductance of model DNA sequences, The Journal of Chemical Physics. New York, American Institute of Physics, 2006, 125: 164704: 1-5.

Shangguan M. and Wang J., Shot noise of charge current and spin current in the presence of Rashba interaction, Nanotechnology. Bristol, IOP Publishing Limited, 2007, 18: 145401: 1-8.

Wang B., Zhu Y., Ren W., Wang J. and Guo H., Spin-dependent transport in Fe-doped carbon nanotubes, Physical Review B. New York, The American Physical Society, 2007, 75: 235415:1-7.

Xing Y.X., Sun Q.F. and Wang J., Symmetry and transport property of spin current induced spin-Hall effect, Phys. Rev. B. 2007, 75: 075324.

Xing Y.X., Sun Q.F. and Wang J., Symmetry and transport property of spin current induced spin-Hall effect, Physical Review B. New York, The American Physical Society, 2007, 75: 075324:1-7.

Researcher : Wang R

List of Research Outputs

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Wang R., Xu S.J., Shi S., Beling C.D., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au/GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 143505: 1-3.

Wang R., Xu S.J., Beling C.D. and Cheung C.K., Response to "comment on influence of indium tin oxide thin-film quality on reverse leakage current of indium tin oxide/n-GaN Schottky contacts [Appl. Phys. Lett. 90, 046101 (2007)]", Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 046102-1.

Researcher : Wang R

List of Research Outputs

Researcher : Wang Y

List of Research Outputs

Li J., Shi S., Wang Y., Xu S.J., Zhao D.G., Zhu J.J., Yang H. and Lu F., Violet electroluminescence of AlInGaN-InGaN multiquantum-well light-emitting diodes: Quantum-confined stark effect and heating effect, IEEE Photonics Technology Letters. IEEE, 2007, 19: 789-791.

Wang Y., Comprehensive optical spectroscopic investigations of GaN epilayers and InGaN/GaN quantum structures. Hong Kong, The University of Hong Kong, 2006, 1-113.

Wang Y., Xu S.J., Zhao D.G., Zhu J.J., Yang H., Shan X.D. and Yu D.P., Non-exponential photoluminescence decay dynamics of localized carriers in disordered InGaN/GaN quantum wells: the role of localization length, Optics Express. Optical Society of America, 2006, 14: 13151-13157.

Researcher : Wang Z

Project Title:	Superconductor science and technology
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Matching Fund for National Key Basic Research Development Scheme (973 Projects)
Start Date:	02/2002

Abstract:

To carry out investigation on superconductor science and technology.

Project Title:	Quantum logic gates based on cyclic geometric phases
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2002

Abstract:

To design a set of quantum logic gates in quantum computing operations with fast running speed based on cyclic geometric phases, which may provide a method to overcome the intrinsic difficulty in adiabatic geometric operations associated with the slow gate speed.

Project Title:	Theoretical studies of impurity and vortex states in high temperature superconductors
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2003

Abstract:

To carry out a systematic and detailed study on the mechanism of IRS in high temperature superconductors(HTS) with particular attention being paid to its magnetic-related origin. It is expected that the study of the variation of IRS with the doping content and accordingly the response of the local moments carried/induced by impurities to the anti-ferromagnetic correlations may help us to clarify the origin of the IRS in HTS; to study theoretically (a) the local electronic structure at vortex cores and the vortex charge in the presence of the orbital AF phase(d-density wave) recently proposed to explain the PG state; and (b) the variation of IRS in response to various spin or charge order parameters by pinning vortices on the imputities as the resonance state is very sensitive to the nature of the electronic structure where the impurity is embedded. In terms of our results, we may be able to understand profoundly some existing experimental results as well as to suggest new experiments to test some predictions.

Project Title:	Vortex state and impurity effect in newly discovered NaCoO superconductors
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003

Abstract:

To study theoretically vortex state and impurity effect in the novel superconductors with triangular lattices.

Project Title:	Theoretical Studies of NaCoO Superconductors
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

To carry out in-depth theoretical studies on the physical quantities related to the low-lying excitation spectrum of this triangular system with emphasis on the effect of disorder to explain profoundly some existing experimental results as well as to suggest new experiments to test some predictions.

Project Title:	Interdisciplinary cutting edge research related to condensed matter physics: solid state quantum computing and quantum information processing
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Matching Fund for NSFC Young Researcher Award
Start Date:	03/2005

Abstract:

To study interdisciplinary cutting edge research related to condensed matter physics: solid state quantum computing and quantum information processing.

Project Title:	Quantum Computation with Solid State Qubits
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2005

Abstract:

The main objectives of this project is: (1) To develop feasible schemes to implement fault-tolerant quantum computation with superconducting and quantum-dot qubits respectively, and to compare our method with other approaches. (2) To address multi-qubit entanglement with superconducting qubits inside a cavity. (3) To study the quantum network based on superconducting qubits coupled with cavities. Very recently, a significant step towards the communication of quantum information, coherent coupling of superconducting qubits with electromagnetic modes has been experimentally demonstrated.

Project Title:	Exploring Quantum Critical Phenomena in Complex Systems
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	02/2006

Abstract:

Quantum entanglement, a key ingredient in quantum information science that does not have a classical counterpart, has attracted increased research interest dramatically for the past years. Recently, quantum entanglement has also been recognized to play an important role in many-body physics. In particular, it has been found to have certain interesting connection with quantum critical phenomena, which are induced by the change of coupling parameters and occur at the absolute zero temperature, in some lower dimensional correlated many-particle systems. So far, several progresses have been achieved in this field, including our work on revealing transition points in one dimensional spin systems with an entanglement entropy scenario. However, for various complex correlated many-body systems in higher dimension or with randomness, how to explore quantum critical phenomena more efficiently and reliably, which can hardly be dealt with by other methods, has been a fundamental and challenging question for a long time. Therefore, it is both important and timely to develop a systematic and model-independent approach for revealing the links between quantum entanglement entropy and quantum critical phenomena, and then to apply it for exploring in depth quantum phase transitions in a variety of correlated systems. In this seed fund project, we shall focus on the following objectives. (1) We plan to develop an efficient general approach for identifying quantum critical points in a wide class of complex correlated systems. We attempt to choose an appropriate entanglement measure to reflect the non-local nature of quantum critical phenomena in correlated lattices. This measure is designed to be an extensive quantity, like the thermal entropy in classical phase transitions, and its variation as functions of coupling parameters will be analyzed carefully, so that a clear connection between its features and quantum critical phenomena can be revealed readily. (2) We intend to investigate some realistic lattice models with randomness or doping, which can hardly be dealt with by other existing methods. Since the present entanglement scenario is expected to better capture the non-local feature of quantum critical phenomena in correlated systems, the size effect in numerical analyses is unimportant, making it be powerful and promising for the future exploration of quantum critical phenomena. It is expected that several initial but significant results/findings will be obtained with international attentions, enabling us to attract successfully external grants to conduct further in-depth research in the exploration of quantum critical phenomena.

Project Title:	Quantum entanglement and quantum phase transitions in correlated systems
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2006

Abstract:

(1) We plan to develop an efficient general approach for identifying and classifying quantum phase transition points in a wide class of strongly correlated systems. We attempt to choose an appropriate entanglement measure to reflect the non-local nature of quantum critical phenomena in correlated lattices. This measure is designed to be an extensive quantity, like the thermal entropy in classical phase transitions, and its variation as functions of coupling parameters will be analyzed carefully, so that a clear connection between its features and quantum phase transitions may be revealed readily. (2) We intend to establish the reliability of our approach by applying it to a number of well-studied systems and comparing with the well-accepted existing results. We then employ the approach to disclose more reliable quantum phase diagrams of several representative correlated models where some results obtained by other methods are still debatable. (3) We attempt to investigate some realistic lattice models with randomness or doping, which can hardly be dealt with by other existing methods. Since the present entanglement scenario is expected to better capture the non-local feature of quantum phase transitions in correlated systems, the size effect in numerical analyses is unimportant, making it be powerful and promising for the future exploration of quantum critical phenomena. It is anticipated that several notable results will be obtained with international attentions, making a timely and significant contribution to the interdisciplinary field of quantum information and correlated many-body physics.

Project Title:	Exploring New Fault Tolerant Quantum Computation Strategies
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	04/2007

Abstract:

Quantum computation has been attracting more and more interests for the past decade because quantum computers can do powerfully many tasks that are intractable for classical computers. Although significant progresses have been achieved, there are still many challenges in physical implementation of quantum computation. To suppress the errors of quantum logic gates is one of them, and is essential to make workable quantum computers. Recently, several promising schemes based on the geometric phases and the topological orders were proposed. In this project, we attempt to achieve the following objectives. (i) We intend to develop for the first time a more efficient but simple adiabatic Abelian geometric quantum computation scheme and to elaborate how to implement this new scheme in several physical systems. (ii) Based on our recent theory for the geometric phase of invariant operators, we attempt to design a universal set of geometric quantum gates. Physical implementation will also be addressed. (iii) We plan to develop a new kind of topological quantum computation strategy, which is expected to be more robust against the errors and has a great potential to increase significantly the fidelity of quantum logic gates.

List of Research Outputs

Researcher : Wang ZD

Project Title:	Superconductor science and technology
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Matching Fund for National Key Basic Research Development Scheme (973 Projects)
Start Date:	02/2002

Abstract:

To carry out investigation on superconductor science and technology.

Project Title:	Quantum logic gates based on cyclic geometric phases
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2002

Abstract:

Project Title:	Theoretical studies of impurity and vortex states in high temperature superconductors
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2003

Abstract:

Project Title:	Vortex state and impurity effect in newly discovered NaCoO superconductors
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	11/2003

Abstract:

To study theoretically vortex state and impurity effect in the novel superconductors with triangular lattices.

Project Title:	Theoretical Studies of NaCoO Superconductors
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

Project Title:	Interdisciplinary cutting edge research related to condensed matter physics: solid state quantum computing and quantum information processing
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Matching Fund for NSFC Young Researcher Award
Start Date:	03/2005

Abstract:

To study interdisciplinary cutting edge research related to condensed matter physics: solid state quantum computing and quantum information processing.

Project Title:	Quantum Computation with Solid State Qubits
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2005

Abstract:

Project Title:	Exploring Quantum Critical Phenomena in Complex Systems
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	02/2006

Abstract:

Project Title:	Quantum entanglement and quantum phase transitions in correlated systems
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2006

Abstract:

Project Title:	Exploring New Fault Tolerant Quantum Computation Strategies
Investigator(s):	Wang ZD
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	04/2007

Abstract:

List of Research Outputs

Bai Y., Li S.S., Zheng H.Z. and Wang Z.D., Detecting a set of entanglement measures in an unknown tripartite quantum state by local operations and classical communication, Physical Review A. New York, The American Physical Society, 2006, 74: 022305:1-8.

Cen L., Wang Z.D. and Wang S.J., Scalable quantum computation in decoherence-free subspaces with trapped ions, Physical Review A. New York, The American Physical Society, 2006, 74: 032321:1-4.

Chen Y., Wang Z.D., Li Y.Q. and Zhang F.C., Spin-orbital entanglement and quantum phase transitions in a spin-orbital chain with SU(2) x SU(2) symmetry, Physical Review B. New York, The American Physical Society, 2007, 75: 195113:1-5.

Du J.F., Zou P. and Wang Z.D., Experimental implementation of high-fidelity unconventional geometric quantum gates using an NMR interferometer, Physical Review A (Rapid Communications). New York, The American Physical Society, 2006, 74: 020302: 1-4.

Li Y., Wang Z.D. and Sun C.P., Quantum criticality in a generalized Dicke model, Physical Review A. New York, The American Physical Society, 2006, 74: 023815:1-5.

Shao L., Wang Z.D. and Xing D.Y., Implementation of quantum gates based on geometric phases accumulated in the eigenstates of periodic invariant operators, Physical Review A (Brief Reports). New York, The American Physical Society, 2007, 75: 014301: 1-4.

Shen R., Chen Y., Wang Z.D. and Xing D.Y., Conservation of spin currents in spin-orbit-coupled systems, Physical Review B. New York, The American Physical Society, 2006, 74: 125313:1-5.

Wang Z.D., Conditional Entanglement (Invited Talk), Forum on Quantum Control and Quantum Information, Forum on Quantum Control and Quantum Information, 2007, ShenZhen . 2007.

Wang Z.D., Croucher Senior Research Fellowship, Croucher Foundation. 2007.

Wang Z.D., Geometric Phases Associated with Invariant and Adiabatic Action Operators (Invited Talk),, Workshop on Frontiers of Quantum Manipulation and Strong Correlation, 2007, Beijing. 2007.

Wang Z.D., Geometric Quantum Computation (Invited Talk), International Conference on Quantum Foundation and Technology, 2006, Hangzhou. 2006.

Wang Z.D., Geometric Quantum Computation (Invited talk), The 1st international symposium on quantum manipulation of photons and atoms, 2007 Beijing. 2007.

Wang Z.D., Multipartite Quantum Entanglement (Invited talk), Workshop on Quantum Control and Quantum Coherence Devices, 2007, Dalian. 2007.

Wang Z.D., Spin-Orbital Entanglement and Quantum Phase Transitions in Spin-orbital Spin-Orbital Entanglement and Quantum Phase Transitions in Spin-Spin-Orbital Entanglement and Quantum Phase Transitions in Spin-orbital Spin-Orbital Entanglement and Quantum Phase Transitions in Spin-orbital Chains Invited Talk) , The 2006 Annual Meeting of Chinese Physical Society, 2006, Beijing. 2006.

Wang Z.D., Sublattice Entanglement and Quantum Phase Transitions (Invited Talk), International Workshop on Frontiers of Theoretical and Computational Physics and Chemistry, 2006, Zhangjiajie. 2006.

Wang Z.D., Understanding Modulation of Local Density of States in Cuprate Superconductors (Invited talk), The 6th International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials, 2007, Sydney (Australia). 2007.

Wang Z.D., Universitas 21 Fellowship, University of Hong Kong. 2007.

Xue Z. and Wang Z.D., Simple unconventional geometric scenario of one-way quantum computation with superconducting qubits inside a cavity, Physical Review A (Brief Reports). New York, The American Physical Society, 2007, 75: 064303: 1-4.

Yao Z., Li J.X. and Wang Z.D., Extended Hubbard model of superconductivity and charge-density-waves in the layered 2H transition metal dichalcogenides, Physical Review B (Brief Reports). New York, The American Physical Society, 2006, 74: 212507: 1-4.

Zhang X.D., Zhang Q. and Wang Z.D., Physical implementation of holonomic quantum computation in decoherence-free subspaces with trapped ions, Physical Review A (Brief Reports). New York, The American Physical Society, 2006, 74: 034302:1-4.

Zhou T., Wang Z.D. and Li J.X., Doping dependence of the spin resonance peak in bilayer high-T_c superconductors, Physical Review B. New York, The American Physical Society, 2007, 75: 024516: 1-6.

Zhou T. and Wang Z.D., High-energy dispersion anomaly induced by the charge modulation in high-T_c superconductors, Physical Review B. New York, The American Physical Society, 2007, 75: 184506: 1-5.

Zhou T., Li J.X. and Wang Z.D., Low-frequency chain and in-plane optical conductivities of detwinned YBa₂Cu₃O_y: Slave-boson mean-field analysis of the t-J model, Physical Review B. New York, The American Physical Society, 2007, 75: 054512: 1-5.

Researcher : Wei Z

List of Research Outputs

Wei Z., Xu S.J. and Li Q., Spontaneous emission mechanisms of GaInAsN/GaAs quantum dot systems, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 124311:1-6.

Wei Z., The optical response of semiconductor self-assembled quantum dots. Hong Kong, The University of Hong Kong, 2006, 1-137.

Researcher : Wong YL

List of Research Outputs

Huang Y., Lu Y., Wong Y.L. and Cheng K.S., A detailed study on the equal arrival time surface effect in gamma-ray burst afterglows, Chinese Journal of Astronomy and Astrophysics. National Natural Science Foundation of China, 2007, 7: 397-404.

Wong Y.L., Huang Y.F. and Cheng K.S., Transient X-ray emission from normal galactic nuclei, Astronomy & Astrophysics. EDP Sciences, 2007, 472: 93-99.

Researcher : Wu H

List of Research Outputs

Wu H., Xu S.J. and Wang J., Impact of the cap layer on the electronic structures and optical properties of self-assembled InAs/GaAs quantum dots, Physical Review B. New York, The American Physical Society, 2006, 74: 205329:1-6.

Researcher : Wu HS

Project Title:	Reference-selective holographic inversion of LEED spectra: a novel method to determine the final atomic structure model
Investigator(s):	Wu HS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	12/2002

Abstract:

The goal of this project is to fully explore the advantages of the direct inversions of LEED spectra and to determine the atomic structures of several interesting systems.

Project Title:	Investigation of pure cubic GaN film growth on SiC(0001) substrate
Investigator(s):	Wu HS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	12/2003

Abstract:

To investigate (1) surface structures of 6H-Sic(0001) surfaces; (2) the interface structures of GaN films/GH SiC(0001); (3) the surface structures of GaN films; (4) the growth condition dependence of the critical thickness of GaN film; (5) the driving force for cubic film growth and inversion from cubic to hexagonal; (6)the possible ways to control the critical thickness of cubic GaN film.

Project Title:	Surface atomic structure extraction from low energy electron diffraction patterson function
Investigator(s):	Wu HS
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	09/2004

Abstract:

A new method named structure extraction from LEED PF is fully implementing by correctly addressing the two issues; (1) a complex system often has PF spots overlap or missing, which makes structure extraction much harder; (2) real systems often have two domains or even more domains in the surface structure, which also makes structure extraction more complicated.

Project Title:	Surface Atomic structure completion from LEED Patterson Function
Investigator(s):	Wu HS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

To figure out a way to deal with unclear or unseen PF spots; to develop an approach to solve the multi-domain problems; to put the modifications into the existing computer program; to test the completed program with more samples; to apply this new method to number of interesting samples to determine their surface atomic structures.

Project Title:	Construct atomic structure models of surfaces with multiple structure phases and disordered over layers by using Low Energy Electron Diffraction Patterson Function
Investigator(s):	Wu HS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2006

Abstract:

To determine surface structures of several GaN films and InN films grown by MBE technique in our lab. The success of these procedures will definitely enhance our capability of solving the tough problem of surface atomic structure determination.

List of Research Outputs

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesis of potassium tungstate micro-walls by thermal evaporation, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 295: 75-78.

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesizing tungsten oxide nanowires by a thermal evaporation method, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 173121: 1-3.

Hong K., Xie M.H. and Wu H.S., Tungsten oxide nanowires synthesized by a catalyst-free method at low temperature, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 4830-4833.

Hu R., Wu H.S. and Hong K., Growth of uniform tungsten oxide nanowires with small diameter via a two-step heating process, Journal of Crystal Growth . 2007, 306: 305.

Liu Y., Wang J., Xie M.H. and Wu H.S., Incommensurate metallic surfactant layer on top of InN film, Surface Review and Letters. World Scientific Pub., 2006, 13: 815-818.

Shi M., Xie M.H., Wu H.S., Wang N. and Tong S.Y., Transition between wurtzite and zinc-blende GaN: An effect of deposition condition of molecular-beam epitaxy, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 151921:1-3.

Wang J., So W.K., Liu Y., Wu H.S., Xie M.H. and Tong S.Y., Observation of a (√3x√3)-R30^o reconstruction on GaN(0001) by RHEED and LEED, Surface Science. Amsterdam, Elsevier B.V., 2006, 600: L169-L174.

Xie M.H., Gong M., Pang K.Y., Wu H.S. and Tong S.Y., Origin of triangular island shape and double-step bunching during GaN growth by molecular-beam epitaxy under excess Ga conditions, Physical Review B. New York, The American Physical Society, 2006, 74: 085314:1-6.

Zheng H., Xie M.H., Wu H.S. and Xue Q.K., Wetting of GaN islands by excess Ga: Origin of different appearances of GaN islands in scanning tunneling microscopy, Physical Review B. New York, The American Physical Society, 2007, 75: 205310:1-5.

Researcher : Xie MH

Project Title:	Structural phase transition of InGaN epi-film during growth on (0001) surface by plasma-assisted molecular-beam epitaxy
Investigator(s):	Xie MH, Wu HS
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2004

Abstract:

To investigate the structural phases of epitaxial InN and GaN films; to examine the possible dependence of crystal structure of the epi-film on the MBE condition; to investigate the physical origin of such a growth phenomenon.

Project Title:	Anomalous temperature dependence of the growth mode and strain in InN/GaN during molecular-beam epitaxy
Investigator(s):	Xie MH
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2005

Abstract:

The project aims at understanding the followings: 1. Alloying between InN and GaN at the heterointerface. In the Stranski-Krastanov (SK) growth of InN on GaN, we shall follow the evolution of volume of the SK-islands under different growth conditions. Comparing to the amount deposited from the flux, I hope that mass transfer from SK-wetting layer and/or GaN substrate to the islands may be established and thereby the extend of alloying at InN/GaN heterointerface be revealed; 2. Effect of surface excess indium layer. Comparion will be made between growth under excess indium and excess nitrogen conditions, so that the effect of surface excess indium adlayer(s) may be noted; 3. Defects in heteroepitaxial InN. The character and density of defects in heteroepitaxial InN layers will be measured, which will be correlated to the state of strain in film.

Project Title:	Growth and properties of AlInN thin films
Investigator(s):	Xie MH
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2006

Abstract:

(1) There exists a large miscibility gap in AlInN alloy and so it is difficult to grow AlInN with arbitrary alloy composition. In this project, the incorporation kinetics of the constituent Al and In elements will be studied. Equipped with such a knowledge, alloys with wide composition ranges will be explored. (2) AlInN grown on GaN represents a unique heteroepitaxial system where the strain can be tuned between compressive and tensile states by changing the alloy composition. Here, an investigation of heteroepitaxial growth mode and the strain effect will be carried out. (3) Finally, characterizations of AlInN epilayers will be conducted for their structural and other physical properties.

List of Research Outputs

Cai X., Djurisic A. and Xie M.H., GaN nanowires: CVD synthesis and properties, Thin Solid Films. Amsterdam, Elsevier B.V., 2006, 515: 984-989.

Cai X., Cheung K.Y., Djurisic A. and Xie M.H., Growth of cubic and hexagonal InN nanorods, Materials Letters. Amsterdam, Elsevier B.V., 2007, 61: 1563-1566.

Dai D., Xu S.J., Shi S., Xie M.H. and Che C.M., Observation of both second-harmonic and multiphoton-absorption-induced luminescence in ZnO, IEEE Photonics Technology Letters. IEEE, 2006, 18: 1533-1535.

Dai X.Q., Wang J.L., Yan H.J., Wu X.H. and Xie M.H., Structural properties of oxygen on InN(0001) surface, Surface Science. Amsterdam, Elsevier B.V., 2007, 601: 2161-2165.

Djurisic A., Leung Y.H., Cheung C.H., Tam K.H., Ng M.C.A., Li D., Wang H., Xie M.H. and Chan W.K., Organic and inorganic nanostructures for optoelectronic devices, Nonlinear Optics and Quantum Optics. Philadelphia, Old City Publishing, Inc., 2007, 37: 99-106.

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesis of potassium tungstate micro-walls by thermal evaporation, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 295: 75-78.

Hong K., Xie M.H., Hu R. and Wu H.S., Synthesizing tungsten oxide nanowires by a thermal evaporation method, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 173121: 1-3.

Hong K., Xie M.H. and Wu H.S., Tungsten oxide nanowires synthesized by a catalyst-free method at low temperature, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 4830-4833.

Liu Y., Wang J., Xie M.H. and Wu H.S., Incommensurate metallic surfactant layer on top of InN film, Surface Review and Letters. World Scientific Pub., 2006, 13: 815-818.

Ning J., Xu S.J., Shi S. and Xie M.H., Slow oscillations in the low-temperature optical reflectance spectra of ZnO: Surface space-charge effect, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 061109: 1-3.

Shi M., Xie M.H., Wu H.S., Wang N. and Tong S.Y., Transition between wurtzite and zinc-blende GaN: An effect of deposition condition of molecular-beam epitaxy, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 151921:1-3.

Tong W.Y., Djurisic A., Xie M.H., Ng M.C.A., Cheung K.Y., Chan W.K., Leung Y.H., Lin H.W. and Gwo S., Metal phthalocyanine nanoribbons and nanowires, Journal of Physical Chemistry B. American Chemical Society, 2006, 110: 17406-17413.

Wang H., Yip C.T., Cheung K.Y., Djurisic A., Xie M.H., Leung Y.H. and Chan W.K., Titania-nanotube-array-based photovoltaic cells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 023508: 1-3.

Wang J., So W.K., Liu Y., Wu H.S., Xie M.H. and Tong S.Y., Observation of a (√3x√3)-R30^o reconstruction on GaN(0001) by RHEED and LEED, Surface Science. Amsterdam, Elsevier B.V., 2006, 600: L169-L174.

Xie M.H., Growth of InN ‘Quantum Dots’ by Molecular-Beam Epitaxy, TMS20007 Annual Meeting, Florida, USA. 2007.

Xie M.H., Initial stage heteroepitaxial growth of InN on GaN(0001) by
molecular-beam epitaxy, International Symposium on Solid State Lighting, China 2006. 2006.

Xie M.H., Gong M., Pang K.Y., Wu H.S. and Tong S.Y., Origin of triangular island shape and double-step bunching during GaN growth by molecular-beam epitaxy under excess Ga conditions, Physical Review B. New York, The American Physical Society, 2006, 74: 085314:1-6.

Zheng H., Xie M.H., Wu H.S. and Xue Q.K., Wetting of GaN islands by excess Ga: Origin of different appearances of GaN islands in scanning tunneling microscopy, Physical Review B. New York, The American Physical Society, 2007, 75: 205310:1-5.

Researcher : Xu H

List of Research Outputs

Kang L., Gao J., Xu H., Zhao S.Q., Chen H. and Wu P.H., Epitaxial Mg₂SiO₄ thin films with a spinel structure grown on Si substrates, Journal of Crystal Growth. Amsterdam, Elsevier B.V., 2006, 297: 100-104.

Researcher : Xu S

Project Title:	Comprehensive spectroscopy investigations of blue and green InGaN/GaN light-emitting diode structures with multi-quantum-wells
Investigator(s):	Xu SJ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2003

Abstract:

The main objective of this project is to understand the luminescence mechanism in the InGaN/GaN LEDs with quantum wells (QWs).

Project Title:	Optical Properties and Electronic Structures of InGaAs/GaAs Self-Assembled Quantum Dots with High Sheet Density
Investigator(s):	Xu SJ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

To gain understanding of the optical properties and electronic structures of high sheet density InGaAs/GaAs self-assembled quantum dots (QDs) through detailed experimental and theoretical investigations.

Project Title:	Multi-photon-excited photoluminescence and dynamic processes of photogenerated carriers in high-quality zinc oxide bulk crystals and nanostructures
Investigator(s):	Xu SJ, Zhao Y
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2006

Abstract:

Thanks to ZnO's large exciton binding energy and potential applications in optoelectronic devices, considerable interest has risen recently on stimulated emission in ZnO thin films and nanostructures at room temperature. Exploitation of optoelectronic applications of ZnO requires a good understanding of various optical processes in ZnO thin films and nanostructures including ultrafast carrier dynamics. At present, very little is known about the multi-photon-absorption-induced luminescence and related issues such as carrier dynamics and the role of exciton-phonon interactions in ZnO. The proposed project aims at understanding mechanisms underlying multi-photon-excited photoluminescence in high-quality ZnO bulk crystals and nanostructures. Following outcomes are to be anticipated from the proposed studies: (1) Enhanced understanding of up-conversion photoluminescence in wide-gap polar semiconductors and related nanostructures.  Determination of characteristic decay times of various luminescence lines of ZnO under excitations of intense femtosecond near-infrared laser employing accurate time-resolved PL techniques.  Improved knowledge on exciton-phonon interactions and their role in the luminescence processes in polar semiconductors with strong exciton-phonon coupling.  Elucidating the role of deep centers in multi-photon excited luminescence processes in wide-gap semiconductors. (2) ZnO in its bulk and nanostructure forms has recently demonstrated great potentials in applications in novel exciton-type optoelectronic devices. As a consequence, up-conversion luminescence in ZnO induced by multi-photon absorption is of particular interest and significance. Detailed investigations of up-conversion luminescence and carrier dynamics in ZnO employing state-of-the-art laser spectroscopic techniques will provide a wealth of knowledge both on fundamental physics and for design and fabrication of innovative optoelectronic devices. We have previously reported what is believed to be the first. (3) observation of intense up-conversion luminescence in bulk ZnO at room temperature in Optics Letters. Building up on the exciting preliminary work, the proposed studies here will expand and deepen our knowledge base in semiconductor photophysics in general and up-conversion photoluminescence of ZnO in particular. Research efforts as proposed here not only help keep Hong Kong at the cutting edge of technological innovations that produce novel optoelectronic devices, but also benefit the Territory by training local graduate students and establishing scientific collaborations with leading experts globally. All these will enhance the international competitive profile of Hong Kong in the scientific arena.

List of Research Outputs

Researcher : Xu SJ

Project Title:	Comprehensive spectroscopy investigations of blue and green InGaN/GaN light-emitting diode structures with multi-quantum-wells
Investigator(s):	Xu SJ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	09/2003

Abstract:

The main objective of this project is to understand the luminescence mechanism in the InGaN/GaN LEDs with quantum wells (QWs).

Project Title:	Optical Properties and Electronic Structures of InGaAs/GaAs Self-Assembled Quantum Dots with High Sheet Density
Investigator(s):	Xu SJ
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

Project Title:	Multi-photon-excited photoluminescence and dynamic processes of photogenerated carriers in high-quality zinc oxide bulk crystals and nanostructures
Investigator(s):	Xu SJ, Zhao Y
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	07/2006

Abstract:

List of Research Outputs

Dai D., Xu S.J., Shi S., Xie M.H. and Che C.M., Observation of both second-harmonic and multiphoton-absorption-induced luminescence in ZnO, IEEE Photonics Technology Letters. IEEE, 2006, 18: 1533-1535.

Jin K. and Xu S.J., Fano resonance in the luminescence spectra of donor bound excitons in polar semiconductors, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 032107: 1-3.

Li J., Shi S., Wang Y., Xu S.J., Zhao D.G., Zhu J.J., Yang H. and Lu F., Violet electroluminescence of AlInGaN-InGaN multiquantum-well light-emitting diodes: Quantum-confined stark effect and heating effect, IEEE Photonics Technology Letters. IEEE, 2007, 19: 789-791.

Li Q., Xu S.J., Li G., Dai D. and Che C.M., Two-photon photoluminescence and excitation spectra of InGaN/GaN quantum wells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 011104: 1-3.

Lui T.Y., Zapien J.A., Tang H., Ma D.D.D., Liu Y.K., Lee C.S., Lee S.T., Shi S. and Xu S.J., Photoluminescence and photoconductivity properties of copper-doped Cd_1-xZn_xS nanoribbons, Nanotechnology. Bristol, IOP Publishing Limited, 2006, 17: 5935-5940.

Ning J., Xu S.J., Shi S. and Xie M.H., Slow oscillations in the low-temperature optical reflectance spectra of ZnO: Surface space-charge effect, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 061109: 1-3.

Wang R., Xu S.J., Djurisic A., Beling C.D., Cheung C.K., Cheung C.H., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 033503: 1-3.

Wang R., Xu S.J., Shi S., Beling C.D., Fung S.H.Y., Zhao D.G., Yang H. and Tao X.M., Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au/GaN Schottky contacts, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 143505: 1-3.

Wang R., Xu S.J., Beling C.D. and Cheung C.K., Response to "comment on influence of indium tin oxide thin-film quality on reverse leakage current of indium tin oxide/n-GaN Schottky contacts [Appl. Phys. Lett. 90, 046101 (2007)]", Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 046102-1.

Wang Y., Xu S.J., Zhao D.G., Zhu J.J., Yang H., Shan X.D. and Yu D.P., Non-exponential photoluminescence decay dynamics of localized carriers in disordered InGaN/GaN quantum wells: the role of localization length, Optics Express. Optical Society of America, 2006, 14: 13151-13157.

Wei Z., Xu S.J. and Li Q., Spontaneous emission mechanisms of GaInAsN/GaAs quantum dot systems, Journal of Applied Physics. New York, American Institute of Physics, 2006, 100: 124311:1-6.

Wu H., Xu S.J. and Wang J., Impact of the cap layer on the electronic structures and optical properties of self-assembled InAs/GaAs quantum dots, Physical Review B. New York, The American Physical Society, 2006, 74: 205329:1-6.

Xu S.J., Luminescence Imaging and Blinking Behavior of Individual InGaN Nanoclusters Formed in GaN Matrix, The 6th Asia-Pacific Conference on Near-Field Optics. 2007.

Xu S.J., New Type of Fano Resonance in Electron Tunneling through a Doped Superlattice, Annual Meeting of Chinese Physics Society 2006. 2006.

Researcher : Xue Z

List of Research Outputs

Xue Z. and Wang Z.D., Simple unconventional geometric scenario of one-way quantum computation with superconducting qubits inside a cavity, Physical Review A (Brief Reports). New York, The American Physical Society, 2007, 75: 064303: 1-4.

Researcher : Yang D

List of Research Outputs

Yang D., Zhang J., Leung J.K.C., Beling C.D. and Liu L.B., Coincidence doppler broadening study in electron-irradiated polyurethane, Nuclear Instruments & Methods in Physics Research (Section B). Amsterdam, Elsevier B.V., 2007, 259: 933-936.

Researcher : Yang K

List of Research Outputs

Yang K., Theoretical study of high transition temperature superconducting Cu-oxide. Hong Kong, The University of Hong Kong, 2006, 1-105.

Researcher : Yao Z

List of Research Outputs

Yao Z., Li J.X. and Wang Z.D., Extended Hubbard model of superconductivity and charge-density-waves in the layered 2H transition metal dichalcogenides, Physical Review B (Brief Reports). New York, The American Physical Society, 2006, 74: 212507: 1-4.

Researcher : Yip CT

List of Research Outputs

Cheung K.Y., Yip C.T., Djurisic A., Leung Y.H. and Chan W.K., Long K-doped titania and titanate nanowires on Ti foil and fluorine-doped tin oxide/quartz substrates for solar-cell applications, Advanced Functional Materials. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 17: 555-562.

Tse C.W., Man K.K.Y., Cheng K.W., Mak S.K., Chan W.K., Yip C.T., Liu Z. and Djurisic A., Layer-by-layer deposition of rhenium-containing hyperbranched polymers and fabrication of photovoltaic cells, Chemistry-A European Journal. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 13: 328-335.

Wang H., Yip C.T., Cheung K.Y., Djurisic A., Xie M.H., Leung Y.H. and Chan W.K., Titania-nanotube-array-based photovoltaic cells, Applied Physics Letters. New York, American Institute of Physics, 2006, 89: 023508: 1-3.

Researcher : Yu D

List of Research Outputs

Yu D., Zhang J., Cheng V.K.W., Beling C.D. and Fung S.H.Y., Doppler broadening of annihilation radiation spectroscopy study using Richardson-Lucy, Maximum Entropy and Huber methods, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3997-4000.

Researcher : Zhang F

Project Title:	Superconductor and antiferromagnetic insulator transition in cuprates and layered organic superconductors
Investigator(s):	Zhang FC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

To gain theoretical understanding of a class of superconductors on the verge of antiferromagnetic insulators. The key issue is to investigate the completition between the electron localization due to electron-electron repulsive force and the delocalized paired electrons due to electron's kinetic energy and the attractive force between electrons originated from the antiferromagnetic spin-spin coupling.

Project Title:	Proposal for Seed Funding for Strategic Research Theme - Computational Physics and Numerical Methods
Investigator(s):	Zhang FC, Cheung PYS, Ching WK, Mok N, Chwang ATY, Sze KY
Department:	Physics
Source(s) of Funding:	Seed Funding for Strategic Research Theme
Start Date:	07/2005

Abstract:

The proposed theme focuses on the computational physics and relevant numerical methodologies, and concentrates the research activities that are of interests to both Faculty of Science and Faculty of Engineering. It includes both the development of the methods and the applications. We intend to develop quantum mechanical methods for complex systems, optimiation techniques such as nonlinear programming, data mining convex programming, and general numerical methods including finite element techniques, large-dimension matrix manipulation and iterative procedures. Using these novel numberical methods together with the existing ones, we would investigate the topics in nano-optics, electrics, transport and mechanics and would also be interested in examine phenomena at larger scales such as structural analysis of continuum systems, soil mechanics, fluid mechanics, crack, fracture and multi-physics problems.

Project Title:	Theory of tunneling conductance and possible checkerboard charge ordering in high temperature superconducting copper oxides
Investigator(s):	Zhang FC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	08/2005

Abstract:

The main objective of this project is to gain theoretical understanding of the checkerboard like electron charge ordering observed in recent scanning tunneling microscopy measurements in high critical temperature (high Tc) superconducting copper oxides.

Project Title:	Exploring novel electronic states in condensed matter
Investigator(s):	Zhang FC, Wang ZD
Department:	Physics
Source(s) of Funding:	Central Allocation Vote - Group Research Project
Start Date:	03/2006

Abstract:

To explore mechanisms that lead to the novel electronic states in condensed matter materials and to develop theories that quantify their physical properties; to explore the intrinsic relation between entanglement and quantum phase transitions; to form a multi-institutional research center in theoretical and computational physics.

Project Title:	Theoretical study of superfluidity in solid helium-4
Investigator(s):	Zhang FC, Ma M
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2006

Abstract:

(1) The purpose of the proposed project is to gain theoretical understanding of recently observed superfluid-like behavior in solid 4-He, or supersolid. At temperature below about 2K, liquid helium enters into a superfluid state and flows without any friction. At a high pressure and a low temperature, helium is solidified. While superflow is intuitively associated with liquid, there have been speculations that solid helium may also show superfluidity due to the zero-point vacancies. However, experiments have since put severe limits on the number of such vacancies and search for the superfluidity in solid helium has not been successful till most recent reports of Kim and Chan on the nonclassical rotational inertial, which shows missing of the mass inertial in rotation, a superfluid-like behavior. The proposed project aims to understand this interesting but puzzling phenomenon. (2) There are two possible scenarios for the superfluidity in solid helium observed in the experiments of Kim and Chan. One is to relate it to zero-point vacancy condensation, a mechanism first proposed by Andreev and Lifshitz in 1969, but experiments since put severe limits on number of vacancies. The other attributes superfluidity to the interfaces within the solid or the interface between the solid and container in the experiment. Currently it is not clear which scenario describes the true physics, and more experiments will be needed to clarify the issue. At this stage of the development, it appears interesting to theoretically examine the possible mechanism for the supersolid based on vacancy or interstitial condensation which is also consistent with the known experiments, namely there is very limited number of vacancies or interstitials in the normal solid state. Since all the theoretical studies have actually ruled out the possible supersolid state without defects, such a mechanism is necessary to explain the possible bulk phenomenon of superfluid in solid helium. Such a study may also be of relevance to Bose Einstein condensation in optical lattices. (3) Since the previous experiments have indicated that single vacancy (or single interstitial) in an otherwise defect-free state is not energetically favorable, one of the key issues in this problem is to examine a new type of lattice defect, or a bound state of vacancy and interstitial called an exciton. We will study coherent motion of helium atoms in a mixture of vacancy, interstitial, and exciton. Our objectives are two-fold as described below. (4) The first objective is to examine a phenomenological lattice model involving both vacancy and interstitial to study the effect of their interactions to the superfluidity and its temperature dependence and impurity effect. (5) The second objective is to study the effect of lattice dynamics to supersolidity within the model. We will study the elastic energy due to the defect and the effect of phonons to the superfluidity in solid helium. (6) The outcome of the project is expected to add our understanding of the defects and the roles they might play in supersolid helium. The experiments in this field are developing rapidly, and we expect more new experiments will provide new insight on this dynamic field. We are flexible and well equipped to tackle related new issues arising during the period of the project as opportunity comes.

List of Research Outputs

Researcher : Zhang FC

Project Title:	Superconductor and antiferromagnetic insulator transition in cuprates and layered organic superconductors
Investigator(s):	Zhang FC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	01/2005

Abstract:

Project Title:	Proposal for Seed Funding for Strategic Research Theme - Computational Physics and Numerical Methods
Investigator(s):	Zhang FC, Cheung PYS, Ching WK, Mok N, Chwang ATY, Sze KY
Department:	Physics
Source(s) of Funding:	Seed Funding for Strategic Research Theme
Start Date:	07/2005

Abstract:

Project Title:	Theory of tunneling conductance and possible checkerboard charge ordering in high temperature superconducting copper oxides
Investigator(s):	Zhang FC
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	08/2005

Abstract:

Project Title:	Exploring novel electronic states in condensed matter
Investigator(s):	Zhang FC, Wang ZD
Department:	Physics
Source(s) of Funding:	Central Allocation Vote - Group Research Project
Start Date:	03/2006

Abstract:

Project Title:	Theoretical study of superfluidity in solid helium-4
Investigator(s):	Zhang FC, Ma M
Department:	Physics
Source(s) of Funding:	Competitive Earmarked Research Grants (CERG)
Start Date:	10/2006

Abstract:

List of Research Outputs

Chen Y., Rice T.M. and Zhang F.C., Atomic scale rotational symmetry breaking in lightly doped Ca_2-xNa_xCuO₂Cl₂, Physica C. Amsterdam, Elsevier B.V., 2007, 460-462: 234-237.

Chen Y., Rice T.M. and Zhang F.C., Rotational symmetry breaking in the ground state of sodium-doped cuprate superconductors, Physical Review Letters. New York, The American Physical Society, 2006, 97: 237004: 1-4.

Chen Y., Wang Z.D., Li Y.Q. and Zhang F.C., Spin-orbital entanglement and quantum phase transitions in a spin-orbital chain with SU(2) x SU(2) symmetry, Physical Review B. New York, The American Physical Society, 2007, 75: 195113:1-5.

Cui X., Shen S.Q., Li J., Ji Y., Ge W.K. and Zhang F.C., Observation of electric current induced by optically injected spin current, Applied Physics Letters. New York, American Institute of Physics, 2007, 90: 242115: 1-3.

Gan J.Y., Chen Y. and Zhang F.C., Superconducting pairing symmetries in anisotropic triangular quantum antiferromagnets, Physical Review B. New York, The American Physical Society, 2006, 74: 094515:1-6.

Huang H.X., Li Y.Q., Gan J.Y., Chen Y. and Zhang F.C., Unconventional superconducting symmetry in a checkerboard antiferromagnet studied via renormalized mean-field theory, Physical Review B. New York, The American Physical Society, 2007, 75: 184523:1-6.

Researcher : Zhang J

List of Research Outputs

Hui C.W., Zhang J., Zhou T., Ling F.C.C., Beling C.D., Fung S.H.Y., Brauer G., Anwand W. and Skorupa W., Positron annihilation study of hydrothermal grown n-type zinc oxide, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Yang D., Zhang J., Leung J.K.C., Beling C.D. and Liu L.B., Coincidence doppler broadening study in electron-irradiated polyurethane, Nuclear Instruments & Methods in Physics Research (Section B). Amsterdam, Elsevier B.V., 2007, 259: 933-936.

Yu D., Zhang J., Cheng V.K.W., Beling C.D. and Fung S.H.Y., Doppler broadening of annihilation radiation spectroscopy study using Richardson-Lucy, Maximum Entropy and Huber methods, Physica Status Solidi C. Weinheim, WILEY-VCH Verlag GmbH & Co., 2007, 4: 3997-4000.

Zhang J., Development of optimized deconvoluted coincidence doppler broadening spectroscopy and deep level transient spectroscopies with applications to various semiconductor materials. Hong Kong, The University of Hong Kong, 2006, 1-239.

Researcher : Zhang Q

List of Research Outputs

Zhang X.D., Zhang Q. and Wang Z.D., Physical implementation of holonomic quantum computation in decoherence-free subspaces with trapped ions, Physical Review A (Brief Reports). New York, The American Physical Society, 2006, 74: 034302:1-4.

Researcher : Zhao H

List of Research Outputs

Zhao H. and Wang J., Photon-assisted shot noise in the mesoscopic system with a toroidal carbon nanotube coupled to normal-metal leads perturbed by ac fields, Physical Review B. New York, The American Physical Society, 2006, 74: 245401:1-11.

Researcher : Zheng D

List of Research Outputs

Zheng D., Leung J.K.C., Lee B.Y. and Lam H.Y., Data assimilation in the atmospheric dispersion model for nuclear accident assessments, Atmospheric Environment. Elsevier Ltd., 2007, 41: 2438-2446.

Researcher : Zheng H

List of Research Outputs

Zheng H., Xie M.H., Wu H.S. and Xue Q.K., Wetting of GaN islands by excess Ga: Origin of different appearances of GaN islands in scanning tunneling microscopy, Physical Review B. New York, The American Physical Society, 2007, 75: 205310:1-5.

Researcher : Zhou B

Project Title:	Spin current, anomalous and spin Hall effects in two-dimensional electron gas with spin-orbit coupling
Investigator(s):	Zhou B, Shen SQ, Zhang FC
Department:	Physics
Source(s) of Funding:	Small Project Funding
Start Date:	09/2006

Abstract:

The objective of this proposed project is to investigate spin coherent transport of two-dimensional electron gas with spin-orbit coupling. Spin coherent transport of conduction electrons in semiconductor heterostructures is currently an emerging subject due to its possible application in a new generation of electronic devices. The coupling between the orbital and spin degree of freedom of electrons is a relativistic effect described by the Dirac equation. The band structure of Zinc-blende III-V semiconductors shows many formal similarities to the situation of free relativistic electrons. The spin-orbit coupling is an important effect in III-V semiconductors which plays a key role in the field of spintronics. There have been considerable concerns on generation of spin current in semiconductors. Spin currents can exist in the form of spin-polarized electrical current, with both a net electrical current and a net spin polarization, or a pure spin current, in which there is no net motion of charge in a pure spin current; spin-up electrons travel in one direction while spin-down electrons travel in the opposite direction. In this project, we will firstly investigate polarized light-induced spin current and how to detect spin current. Optical injection of spin current is an alternative way and largely based on the fact that the spin polarized carriers in conduction band can be injected in semiconductors via absorption of the circularly or linearly polarized light. Optical processes rely on the spin-orbit interaction, which allow the electric field of incident light to couple to the spin degree of freedom. It is well known that the orientation of electron spins in semiconductors by interband optical transitions, due to the absorption of circularly polarized light, leads to the generation of a net spin density in semiconductors. Recently, there have been considerable efforts to achieve spin polarized current in semiconductors by means of optical injection. The conversion of the carriers' spin polarization into an electric current has been observed in both n-type and p-type quantum wells as well as for different symmetry classes. Recently, spin photocurrent was also experimentally demonstrated in a two-dimensional electron gas system with Rashba spin splitting. Besides spin polarized current, it is more interesting to generate pure spin current. Pure spin current from one-photon absorption of linearly polarized light has proposed and observed. In this project, we consider that the semiconductor wells are irradiated by polarized lights to induce spin polarization, electric current and pure spin current via interband excitations. Under oblique incidence of circularly polarizaed light, in-plane spin polarization can be induced as well as z-component spin polarization, and due to spin-orbit coupling photocurrent can be also induced in the plane of a quantum well perpendicular to the direction of light propagation. The effect is just like the converse effect of electric current-indeuced spin polarization in 2D system without inversion symmetry. Additionally, a pure spin current occurs perpendicularly to the direction of photocurrent. The linearly polarized light being normally incident on the sample surface can produce pure spin currents with an in-plane polarization, while there are no spin ploarization and electric current. We expect to establish the relation between light-induced electric current and pure spin current in semiconductor quantum wells via inter-band transitions, and more to propose that linearly polarized light-induced pure spin current can be determined by measuring the photocurrent. Secondly, we will investigate the anomalous Hall effect in two-dimensional hole gas with magnetic impurities. The theory of anomalous Hall effect has a long history since 1950s. It was realized that several different mechanisms are contributed to the total Hall conductance in ferromagnetic metals and semiconductors. Except for the skew scattering and the side jump from the impurity scattering, an intrinsic mechanism tells that the spin-orbit coupling in the electronic band structure of the system may induce a non-zero Berry phase or magnetic monopole in the momentum space and cannot be neglected in the transverse transport of electrons, especially in the diluted magnetic semiconductors. On the other hand, the spin aspect of transverse transport was also studied recently, in which an external electric field may drive electrons to form a transverse spin current in the systems with spin-orbit coupling even in paramagnetic electronic systems. These two effects reflect the charge and spin aspects of electron transport, respectively, and have some common features as their physical origin stems from the same spin-orbit coupling of conduction electrons. More and more experiments support the intrinsic mechanism. In this project, based on two-dimensional Luttinger model, Hall conductivity will be calculated numerically with variation of experimental parameters. We will investigate sign change of Hall conductivity. Finally, we will investigate spin Hall effect on [110] and [111] semiconductor quantum wells with inversion asymmetry. The spin Hall effect is the generation in a paramagnetic system of spin current perpendicular to an applied charge current leading to a spin accumulation with opposite magnetization at each edge. This effect was first predicted over three decades ago. Spin Hall effect can be used for efficiently injecting spin current into semiconductors. There are two kinds of spin Hall effects: one is the extrinsic spin Hall effect due to spin-dependent impurity scattering; the other is the intrinsic spin Hall effect, which is entirely due to spin-orbit coupling terms in the single-particle carrier Hamiltonian and occurs even in the absence of any impurity scattering process. The intrinsic spin Hall effect has received a great deal of theoretical attention recently. However, current theories predict that the intrinsic spin Hall effect can be strongly be suppressed by disorder effects. Especially, the intrinsic spin Hall effect disappears vanishes in the bulk of a Rashba-split two-dimensional electron gasd due to effect of disordered, if only considering k-linear terms of spin-orbit coupling. On the other hand, Chao etal presented that when Dresselhaus interaction including k-cubic terms of spin-orbit coupling is taken into account, spin Hall current is not zero even in presence of disorder. In this project, we consider [110] and [111] semiconductor quantum wells with inversion asymmetry. It is expected that spin Hall effect survives due to k-cubic terms of spin-orbit coupling in these semiconductor.

List of Research Outputs

Zhou B. and Shen S.Q., Deduction of pure spin current from the linear and circular spin photogalvanic effect in semiconductor quantum wells, Physical Review B. New York, The American Physical Society, 2007, 75: 045339: 1-6.

Researcher : Zhou T

List of Research Outputs

Hui C.W., Zhang J., Zhou T., Ling F.C.C., Beling C.D., Fung S.H.Y., Brauer G., Anwand W. and Skorupa W., Positron annihilation study of hydrothermal grown n-type zinc oxide, 14th International Conference on Positron Annihilation, 23-28 July 2006, Hamilton. 2006.

Zhou T., Wang Z.D. and Li J.X., Doping dependence of the spin resonance peak in bilayer high-T_c superconductors, Physical Review B. New York, The American Physical Society, 2007, 75: 024516: 1-6.

Zhou T. and Wang Z.D., High-energy dispersion anomaly induced by the charge modulation in high-T_c superconductors, Physical Review B. New York, The American Physical Society, 2007, 75: 184506: 1-5.

Zhou T., Li J.X. and Wang Z.D., Low-frequency chain and in-plane optical conductivities of detwinned YBa₂Cu₃O_y: Slave-boson mean-field analysis of the t-J model, Physical Review B. New York, The American Physical Society, 2007, 75: 054512: 1-5.

Researcher : Zhou T

List of Research Outputs

Researcher : Zhu Y

Project Title:	Magnetism and Magneto-resistance in Carbon Nanotube / Transition Metal Hybrid System
Investigator(s):	Zhu Y
Department:	Physics
Source(s) of Funding:	Seed Funding Programme for Basic Research
Start Date:	06/2006

Abstract:

Spintronics aims at using the spin of electrons to carry information [1]. The simplest spintronics device is spin-valve, which consists of two ferromagnetic electrodes sandwiched with a layer of nonmagnetic metal or insulator. The junction resistance can be manipulated with a relative small magnetic field due to spin polarization at the Fermi energy. Transition metals are widely used to grow magnetic thin films and fabricate spin-valve. On the other hand, one-dimensional nano-devices are desirable in some application circumstances. Especially, carbon nanotubes are well studied for their physical properties and show great potential as building blocks in nanoscale electronics [2]. Experimentally, carbon nanotubes can either be filled with materials in its cavity or be coated with materials on the tube surface [3,4]. A combination of carbon nanotubes and ferromagnetic transition metals could be promising in providing the required magnetism, dimensionality, and small volume. Transport measurements on multi-wall carbon nanotubes coupled to ferromagnetic electrodes showed maximum magneto-resistance of 9%, from which the spin-flip scattering length is estimated to be at least 130 nm [5]. Pronounced gate-field-controlled magneto-resistance was observed in carbon nanotubes connected by ferromagnetic leads. Both the magnitude and the sign of the magneto-resitance can be tuned with gate voltages [6]. However, there are only a few theoretical works for the properties of carbon nanotube / transition metal hybrid systems [7,8]. Very recently, Yang et al found through ab initio calculation that ferromagnetic materials packed inside carbon nanotubes exhibit substantial magnetism and strong spin polarization at the Fermi level [8]. Motivated by their work, we propose to study the transport properties in the magnetic junctions composed of carbon nanotube and transition metals. The objective of this project is summarized as follows: (1) Develop and apply the new version of matdcal package to model spin-dependent transport. The new version adopts k point sampling in the xy-plane to simulate multi-layer structures; Both local spin density approximation (LSDA) and generalized gradient approximation (GGA) are implemented in the exchange correlation energy; partial core correction and optimized Siesta orbitals are used in the calculation. (2) Investigate the magnetism of quasi 1D ferromagnetic wire and its effects on the magneto-resistance. Several questions are to be answered: How does the magnetism evolves from 3D bulk to quasi 1D wire? How does the coupling between carbon nanotube and ferromagnetic atoms change the magnetism? What is the magneto-resistance in some possible geometries (e.g., carbon nanotube filled or coated with cobalt atoms)? Whether the singularity in density of states of 1D system enhances the spin polarization at the Fermi level? [1] G. A. Prinz. Cience 282, 1660 (1998). [2] M. S. Dresselhaus, G. Dresselhaus, and P. Avouris, Carbon Nanotubes: Synthesis, Structure, Properties and Applications (Springer-Verlag, Berlin, Germany, 2001). [3] M. Monthious, Carbon 40, 1809 (2002). [4] Y. Zhang and H. Dai, Appl. Phys. Lett. 77, 3015 (2000). [5] K. Tsukagoshi, B. W. Alphenaar, and H. Ago, Nature (London) 401, 572 (1999). [6] S. Sahoo et al, Nature Physics 1, 99 (2005). [7] H. Mehrez, J. Taylor, H. Guo, J. Wang, and C. Roland, Phys. Rev. Lett. 84, 2682 (2000). [8] C.-K. Yang, J. Zhao, and J. P. Lu, Phys. Rev. Lett. 90, 257203 (2003).

List of Research Outputs

Ren W., Reimers J.R., Hush N.S., Zhu Y., Wang J. and Guo H., Models for the structure and electronic transmission of carbon nanotubes covalently linked by a molecular bridge via amide couplings, The Journal of Physical Chemistry C. American Chemical Society, 2007, 111: 3700-3704.

Wang B., Zhu Y., Ren W., Wang J. and Guo H., Spin-dependent transport in Fe-doped carbon nanotubes, Physical Review B. New York, The American Physical Society, 2007, 75: 235415:1-7.

-- End of Listing --