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COLLOQUIA & SEMINARS 2010:
 

1. (SEMINAR)"Supersolidity due to vancancies in a bosonic solid", Prof. Dr. Yu Shi (Fudan University), at 4:00 pm, March 8, 2010.

1. Abstract:
   We discuss supersolidity as a consequence of off-diagonal long-range order (ODLRO) in an interacting Bose system. For a class of variational wavefunctions used for solid helium, there is no ODLRO or supersolidity, even though there exist zero-point motion and exchange effect. In particular, we consider the presence of vacancies, and study the Hartree-Fock wave function built up from localized wave functions of single atoms, with nearest neighboring overlap. The zero-momentum particle number is expressed in terms of permanents of matrices. It is found that the condensate fraction is proportional to and of the same order of magnitude as that of the vacancy concentration, hence there is ODLRO when the number of vacancies is a finite fraction of the number of the lattice sites.

2. (COLLOQUIUM)"Atomic and molecular processes in high energy density matter", Dr. Jian-Guo Wang (Institute of Applied Physics and Computational Mathematics), at 4:00 pm, March 25, 2010.

1. Abstract:
   High energy density (HED, >10^{11}J/m3) matter widely exists in the astrophysical environments (Big Bang, supernova and solar core, etc), inertial confined fusion, strong shock wave and nuclear weapons. The physics at these extreme conditions is becoming a new frontier for science and technology. The knowledge of atomic and molecular physics is essential for simulation and diagnostics of HED matter. In this talk, we review the research advance on the atomic and molecular processes in HED matter.

3. (COLLOQUIUM)"Spin-Density-Wave and Superconductivity in Electron Doped Iron-Pnictide Superconductors", Prof. Dr. C. S. Ting (University of Houston, USA), at 4:00 pm, March 29, 2010.

1. Abstract:
   The coexistence of the spin-density-wave (SDW) and superconductivity in electron-doped iron-pnictide superconductors such as Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ is studied using a two orbital model which qualitatively reproduces some of the ARPES experimental measurements. Based on the Bogoliubov-de Gennes equations and mean field theory, the phase diagram is mapped out and the evolution of the Fermi surface as the doping varies will be presented. The local density of states (LDOS) has also been calculated from low to high doping. We show that the strength of the superconducting coherent peak at the positive energy gets enhanced and the one at the negative energy is suppressed by the SDW order in the underdoped region. The obtained results are in good agreement with several ARPES and STM experiments. In addition, the doping dependence of the dynamic spin susceptibility is investigated under RPA approximation. Our results for the spin susceptibility are also in good agreement with several neutron scattering experiments in various doping ranges at temperatures above and below the superconducting transition temperature. For the overdoped sample where one of the two hole pockets around $\Gamma$ point disappears according to ARPES, we show that the imaginary part of the spin susceptibility in both SC and normal phases exhibits a gap-like behavior.

4. (SEMINAR)"Build of New Chalcogenide Heterostructures and Prospect of Potential Applications", Prof. Dr. Hui-Zhen Wu (Zhejiang University), at 4:00 pm, April 1, 2010.

1. Abstract:
   Lead chalcogenides are narrow gap semiconductors that had device applications in mid-infrared light sources and infrared detector arrays respectively for molecular spectroscopy and infrared imaging. However, these devices are limited to operate only at low temperatures in most cases. In recent years, much effort has been dedicated on the quest for improvement of the material system and related devices. PbTe/CdTe heterostructures that are nearly lattice-matched may be promising for both optoelectronics and spintronics. PbTe/CdTe heterostructures (QWs and QDs) have been synthesized by molecular beam epitaxy and a highly asymmetric energy band with type-I band alignment was concluded using x-ray photoelectron spectroscopy. The realization of PbTe/CdTe quantum structures and the highly asymmetric energy band make it possible to construct asymmetric CdTe/PbTe/Pb16Ó1xSrxTe QWs for the probe of spintronics. Contrary to HgTe/CdTe QWs, the spin-orbit interaction in the CdTe/PbTe/Pb16Ó1xSrxTe QWs is purely Rashba and anisotropic. Rashba splittings in the asymmetric QWs with different growth orientations and electron densities was explored.

5. (SEMINAR)"Coulomb screening and collective excitations in biased bilayer graphene", Prof. Dr. X. F. Wang (Soochow University), at 4:00 pm, April 8, 2010.

1. Abstract:
   We have investigated the Coulomb screening properties and plasmon spectrum in a bilayer graphene under perpendicular electric bias. The bias voltage applied between the two graphene layers opens a gap in the single particle energy spectrum and modifies the many-body correlation and collective excitations. The energy gap can soften the plasmon modes and lead to the crossover of plasmon from a Landau damped mode to undamped one. Plasmon modes of long lifetime may be observable in experiments and may have application potential.

6. "Tibetan Culture and Arts", Mr. Ciren Duojie (Vice Chairman of Tibeten Artists Association), at 4:00 pm, May 6, 2010.
   

7. (COLLOQUIUM)"Repulsive pairing in many-body interacting system and the extended Hubbard model", Prof. Dr. Jiu-Qing Liang (Institute of Theoretical Physics, Shanxi University), at 4:00 pm, May 20, 2010.

1. Abstract:
   We propose a Hamiltonian of ultracold atoms in optical lattices including the two-body interaction of nearest neighbors, which reduces to the Bose-Hubbard model in weak-interaction limit. An atom-pair hopping term appearing in the Hamiltonian explains naturally the recent experimental observation of correlated tunneling in a double-well trap with strong atom-atom interactions and moreover leads to a dynamic process of atom-pair tunneling where strongly interacting atoms can tunnel back and forth as a fragmented pair. A new dynamic state of oscillations induced by the atom-pair tunneling is found in the strong interaction regime, where the Bose-Hubbard model gives rise to the insulator state with fixed time-averaged value of atom-occupation number only. Quantum phase transitions between two quantum phases characterized by degenerate and nondegenerate ground states are shown to be coinciding with the Landau second-order phase-transition theory. New repulsive bound-state solutions of atom-pair in a one-dimension optical lattice are found explicitly. We also show the rich phase diagrams of supersolid and pair-superfluid phases.

8. (Ph. D. Dissertation Defense)"Spin Dynamics in III-V Semiconductors and Their Nanostructures", Mr. J. H. Jiang, [Committee Members: Prof. Bang-Fen Zhu (Chair, Academician, Tsinghua Univ.); Prof. Dr. Xi Dai (IOP); Prof. Dr. You-Quan Li (Zhejiang Univ.); Prof. Dr. Giovanni Vignale (Univ. Missouri-Columbia); Prof. Ding-Sheng Wang (Academician, IOP); Prof. Dr. Ya-Yu Wang (Tsinghua Univ.); Prof. Jian-Bai Xia (Academician, Inst. Semicond.); Prof. Dr. Tao Xiang (IOP)], at 2:00 pm, June 13, 2010.
   

9. (SEMINAR)"A robust semi-empirical Hamiltonian for large-scale simulations of complex nanostructures", Assis. Prof. Dr. Ming Yu (University of Louisville, USA), at 10:00 am, June 14, 2010.

1. Abstract:
   In this talk, I will introduce a robust semi-empirical Hamiltonian for large-scale simulations of complex nanostructures developed by the condensed mater theory group at University of Louisville. The Hamiltonian, referred as self-consistent (SC) and environment-dependent (ED) Hamiltonian, is developed in the framework of linear combination of atomic orbitals (LCAO) and includes multi-center electron-ion and electron-electron interactions. Linear scaling and parallel algorithms for large-scale simulations of materials have also been incorporated. The present approach goes beyond the traditional two-center tight-binding Hamiltonians in terms of its accuracy and transferability and allows the study of system sizes that are beyond the scope of ab-initio simulations. We have studied a wide-variety of complex materials and complex phenomena using the SCED-LCAO approach. I will present some of our recent results in this talk including (i) the phase transformations of carbon clusters upon annealing, (ii) the bucky-diamond structure of SiC clusters, and (iii) the morphology and stability of SiC nanowires. The successful outcome of these case studies is a testament to the transferability and the predictive power of the Hamiltonian to different types of atomic environments (i.e., co-ordinations and bonding configurations).

10. (SEMINAR)"Coulomb drag and spin Hall Drag: new coupling mechanisms for nanoelectronics", Prof. Dr. Giovanni Vignale (University of Missouri-Columbia, USA), at 4:00 pm, June 14, 2010.

1. Abstract:
   Double-layer structures consisting of two parallel quantum wells separated by a narrow potential barrier are an important class of nanoscale electronic devices. Each layer hosts a quasi-two dimensional electron gas and electrons interact across the barrier via the Coulomb interaction. When an electric current is driven in one of the layers the Coulomb interaction causes a charge accumulation in the other layer. This phenomenon, known as Coulomb drag, is of fundamental interest as a probe of electron correlations and provides a new coupling mechanism between spatially separated elements of nano-electronic circuits, alternative to the conventional inductive and capacitive couplings. A second effect of great interest is the Spin Hall Effect, i.e. the generation of spin accumulation by an electric current. This is due to spin-orbit interactions and has recently received great attention not only because of its theoretical subtlety but also for its usefulness as a source of spin-polarized currents. In this talk I review our current understanding of these two effects and I describe a third one, which arises from the combination of spin Hall effect and Coulomb drag. I call it Spin Hall Drag. The effect consists in the generation of transversal spin accumulation in one layer by an electric current in the other layer. Microscopic calculations indicate that the induced spin accumulation, although considerably smaller than the one observed in the ordinary spin Hall effect, is large enough to be detected in optical rotation experiments.

11. (SEMINAR)"Spin-injection into GaAs layers" , Prof. Dr. Dieter Weiss (Universitaet Regensburg, GERMANY), at 4:00 pm, June 15, 2010.

1. Abstract:
   Electrical spin-injection and detection is a conditio sine qua non for semiconductor spin-tronics. Here we demonstrate electrical injection and detection of spin-polarized electrons in a single wafer, all-semiconductor, GaAs-based lateral spintronic device, employing p+-(Ga,Mn)As/n+-GaAs ferromagnetic Esaki diodes as spin aligning contacts [1]. As (Ga,Mn)As is a hole conductor, electrical spin injection into a n-type GaAs transport channel involves conversion of spin polarized holes into spin-polarized electrons via Esaki tunneling which leaves its mark in a characteristic bias dependence of the spin-injection efficiency. The maximum spin-injection efficiency at low temperatures is so far 50%. Due to spin-orbit in-teraction the spin polarization is anisotropic with respect to different crystallographic di-rections [2]. We observe an in-plane anisotropy of 8% in case of spins oriented either along or [110] directions and 25% anisotropy between in-plane and perpendicular-to-plane orientation of spins [3]. Apart from transport experiments we also probed the spin-polarization employing spatially resolved magneto-optical Kerr measurements. By cleaving the sample the spin-polarization can also be mapped underneath a contact [4].
   Work carried out in collaboration with Andreas Einwanger, Mariusz Ciorga, Roland Voelkl, Tobias Korn, Christian Schueller, Ursula Wurstbauer, Dieter Schuh, Werner Wegscheider, Bernhard Endres, Frank Hoffmann, Christian Back and Guenther Bayreuther,
   [1] M. Ciorga, A. Einwanger, U. Wurstbauer, D. Schuh, W. Wegscheider, and D. Weiss, Phys. Rev. B 79, 165321 (2009).
   [2] P. Sankowski, P. Kacman, J. A. Majewski, and T. Dietl, Phys. Rev. B 75, 045306 (2007).
   [3] A. Einwanger, M. Ciorga, U. Wurstbauer, D. Schuh, W. Wegscheider and D. Weiss, Appl. Phys. Lett. 95, 152101 (2009)
   [4] P. Kotissek, M. Bailleul, M. Sperl, A. Spitzer, D. Schuh, W. Wegscheider, C. H. Back and G. Bayreuther, Nature Physics 3, 872 (2007)

12. (SEMINAR)"Spinning Electrons", Asso. Prof. Dr. R. Winkler (Northern Illinois University and Argonne National Laboratory, USA), at 10:00 am, June 22, 2010.

1. Abstract:
   Spin-orbit coupling makes the electron spin degree of freedom respond to its orbital environ- ment. Thus it gives us a "control knob" with which we can steer the purely quantum-mechanical spin degree of freedom. Recently, the electron spin and spin-orbit coupling have attracted much attention due to the possibility to complement conventional charge-based electronics by novel approaches that use also the electron's spin (spintronics).
   In my talk I will provide a general introduction into the world of spinning electrons [1], followed by the discussion of a few examples for the rich and fascinating physics that emerges from the interplay between the spin and orbital dynamics of electrons in solids. Similar to an external magnetic field, spin-orbit coupling can give rise to spin precession. In the presence of a driving electric field the steady-state nonequlibrium density matrix contains a precessing component describing the formation of spin currents. A second nonequilibrium component which does not precess turns out to be responsible for the electric generation of spin densities [2].
   A decomposition of the spin-orbit coupled dynamics in multiple bands into a smooth part and an oscillatory part is well-known from relativistic quantum mechanics, where an oscillatory component in the orbital dynamics has been called zitterbewegung. We will show that the generation of spin currents and spin densities in semiconductors is closely related with the phenomenon of zitterbewegung of Dirac electrons [3].
   [1] R. Winkler, Spin-Orbit Coupling Effects in Two-Dimensional Electron and Hole Systems (Springer, Berlin, 2003).
   [2] D. Culcer and R. Winkler, Phys. Rev. Lett. 99, 226601 (2007).
   [3] R. Winkler, U. Z \u0308licke, and J. Bolte, Phys. Rev. B 75, 205314 (2007). u

13. (SEMINAR)"Time reversal of a pseudo-spin: General properties and application to graphene", Asso. Prof. Dr. Ulrich Zuelicke (Massey University, NEW ZEALAND), at 4:00 pm, June 22, 2010.

1. Abstract:
   Two-level systems are routinely represented in terms of pseudo-spin-1/2 degrees of freedom, and such pseudo-spins are usually considered to be entirely analogous to the real spin angular momentum. Here we consider time reversal (TR) of pseudo-spins from a completely general perspective and find that there exist two different types. One type behaves like ordinary spin, for which all of its three Cartesian components are odd under TR. In addition, a second type of pseudo-spin exists, behaving counter-intuitively in that only one Cartesian component is odd and the other two are even under TR. The second type is not merely of academic interest, as it is realised, eg, by the pseudo-spin representation of the 2D isotropic harmonic oscillator (Schwinger model of spin-1/2). We show that the sublattice-related pseudospin of quasi-relativistic charge carriers in graphene also belongs to the second type and discuss observable implications of this fact.

14. (SEMINAR)"From Quantum Hall Effect to Topological Insulators", Researcher Dr. Yong-Qin Li (IOP), at 4:00 pm, June 29, 2010.

1. Abstract:
   In this talk, a brief review of the quantum Hall effect will be given with emphasis on its relevance to the topological order. It follows an introduction to spin physics in the fractional quantum Hall regime, in which the competition between electron-electron interaction and Zeeman energy gives rise to extraordinarily rich phenomena. Some of the latest developments in the spin physics in the half-filled Landau levels will be discussed, including the spin polarization of the 5/2 state, which has been argued to be a basis for topological quantum computation. Finally, recent progress in 3D topological insulators will be presented. In particular, field effect devices based on bismuth selenide (Bi2Se3) developed in Dan Tsui Laboratory will be described in detail.

15. (SEMINAR)"Electron spin decoherence in nanostructures", Prof. Dr. E. L. Ivchenko (Ioffe Institute, RUSSIA), at 4:00 pm, July 13, 2010.

1. Abstract:
   The talk presents the results of recent experimental and theoretical studies of electron spin dynamics.
   1. Introduction. Optical Orientation of Free Carriers and Excitons. Generation of carrier spin coherence by circularly polarized laser pulses: (a) empty QW, only photogenerated carriers which form excitons; (b) low density two-dimensional electron gas (2DEG), trions with a singlet ground state formed by a photogenerated exciton and a resident electron; (c) dense 2DEG with a Fermi energy exceeding the exciton binding energy.
   2. Spin Faraday and Kerr Rotation Technique. The pump-probe technique serves as a very convenient tool to study the coherent spin dynamics. A short circularly polarized pump pulse generates the electron spin orientation, which is monitored by the weaker linearly polarized probe pulse delayed in respect to the pump one. In external magnetic elds a coherent spin precession of the electrons can be detected opening an access to the electron spin dephasing times.
   3. Decoherence and Dispersion of Electron g Factors in Quantum-Dot Arrays. The formalism presented provides a complete theoretical description of single- and twocolor pump-probe Faraday or Kerr rotation experiments in an ensemble of singly charged quantum dots (QDs). The modeling of time-dependent traces of the Faraday rotation signal shows their high sensitivity to the inhomogeneous properties of the QD ensemble, such as the transition-frequency dependence of electron g-factor and the nuclear-induced dispersion, as well as to the excitation conditions, such as pump and probe pulse detuning, single pulse versus train of pulses excitation, and the pumping intensity.
   4. Decoherence of Neutral Zero-Dimensional Excitons. Entangled Photons. A quite general property of actual QDs is the existence of a splitting of the exciton radiative doublet into linearly polarized components due to an anisotropic contribution in the electronhole exchange interaction. In some circumstances the Zeeman effect and the orbital effect of an in-plane magnetic field can lead to a cancellation of the native anisotropic splitting. This allows one to produce polarization-entangled photon pairs in the quantum-dot biexcitonexciton radiative cascade.
   5. Spin Relaxation Controlled by Electron-Electron Interaction. In high-mobility quantum wells, the electron-electron interaction controls the Dyakonov-Perel spin relaxation. In a weakly spin polarized electron gas, the spin relaxation rate is limited by electronelectron collisions. In a highly polarized gas, the spin is stabilized by the exchange interaction: the Hartree-Fock exchange eld acts as an external magnetic eld and suppresses the Dyakonov-Perel' spin relaxation.

16. (SEMINAR)"Optical injection and evolution of charge and spin currents in quantum wells", Prof. Dr. E. Ya. Sherman (Universidad del Pais Vasco and IKERBASQUE Basque Foundation for Science, Bilbao, SPAIN), at 4:00 pm, July 14, 2010.

1. Abstract:
   We consider optically injected charge and spin currents in semiconductor quantum wells. The injection can be done by quantum optics techniques with the interference of the one- and two-photon transition processes, by intersubband light absorption, and by a stimulated Raman process. The final state with the injected currents strongly depends on the injection process, producing the system very strongly out of the equilibrium for the interband transitions and relatively weakly out of the equilibrium for the Raman process. In addition to the directly injected, the resulting spin currents can arise due to the spin-dependent scattering of electrons by excited holes. The resulting patterns of charge and spin densities will be analyzed. We show that the charge current evolution can have a universal character, independent on the system details.

17. (SEMINAR)"One dimensional polaritons in a ZnO microwire", Prof. Dr. Zhang-Hai Chen (Fudan University), at 4:00 pm, September 10, 2010.

1. Abstract:
   A cavity-polariton, formed due to the strong coupling between exciton and cavity mode, is one of the most promising composite bosons for realizing macroscopic spontaneous coherence at high temperature. Up to date, most of the experimental observations of polariton condensation were carried out in two-dimensional (2D) planar microcavities in which light field was confined one dimensionally [1-5]. However, the role of dimensionality in coherent quantum degeneracy of composite bosonic system of exciton polariton remains mysterious. Here we show the experimental observation of the room temperature one-dimensional (1D) polariton condensate in a ZnO microwire. A massive occupation of the polariton ground state above a distinct pumping power threshold is clearly demonstrated by using the angular resolved spectroscopy under non-resonant excitation. The power threshold is one order of magnitude lower than that of Mott transition. A well-defined far field emission pattern from the polariton condensate mode is clearly observed, manifesting the coherence build-up in the condensed polariton system.
   
   [1] J. Kasprzak, et al., Bose-Einstein condensation of exciton polaritons. Nature 443, 409 (2006).
   [2] R. Balili, V. Hartwell, D. Snoke, L. Pfeiffer & K. West, Bose-Einstein condensation of microcavity polaritons in a trap, Science 316, 1007 (2007).
   [3] Daniele Bajoni, et al., Polariton laser using single micropillar GaAs-GaAlAs semiconductor cavities, Phys. Rev. Lett. 100, 047401 (2008).
   [4] K. G. Lagoudakis, et al., Quantized vortices in an exciton-polariton condensate, Nature Phys. 10, 1038 (2008).
   [5] A. Amo, et al., Collective fluid dynamics of a polariton condensate in a semiconductor microcavity, Nature, 475, 291-295 (2009).
   [6] Liaoxin Sun, Zhanghai Chen et al, Direct observation of whispering gallery mode polaritons and their dispersion in a ZnO tapered microcavity, Phys. Rev. Lett. 100, 156403 (2008).
   [7] A. Trichet, Liaoxin Sun, G. Pavlovic, N. A. Gippius, G. Malpuech, W. Xie, Zhanghai Chen, M. Richard and Le Si Dang, arXiv: 0908.3838.

18. (COLLOQUIUM)"Ultrafast and nonlinear terahertz spectroscopy of semiconductor quantum structures", Prof. Dr. Harald Schneider (Institute of Ion-Beam Physics and Materials Research, Forschungszentrum Dresden Rossendorf, Dresden, GERMANY), at 2:30 pm, September 21, 2010.

1. Abstract:
   This talk gives an overview on our recent experimental studies involving terahertz (THz) radiation from photoconducting antennae and from the free-electron laser in Dresden, Germany. In particular, microstructured scalable antennae for photoconductive THz emitters and semiconductor quantum well detectors for quadratic autocorrelation of pulsed THz radiation will be discussed. The final part of my talk will concentrate on nonlinear THz spectroscopy, in particular THz sideband generation and coherent dynamics of excitons dressed by strong THz beams.

19. (SEMINAR)"Spin States and Spin correlation in Semiconductor Quantum Dots", Prof. Dr. H. Q. Xu (Lund University, SWEDEN), at 4:00 pm, September 21, 2010.

1. Abstract:
   I will report our recent studies of spin physics and spin-correlation phenomena in semiconductor quantum dots. The devices were fabricated from InGaAs/InP semiconductor heterostructures and from InSb semiconductor nanowires. Spin states, effective g-factors, spin-orbit interaction energy, and exchange energy were measured for the fabricated quantum dots. We also studied strong correlation phenomena in the fabricated quantum dot devices. In addition to both odd-number electron and even-number electron Kondo effects, we observed a new spin-correlation-induced phenomenon in InSb quantum dot devices, namely the conductance blockade at the degeneracy of two orbital states with the same spin. We attribute this conductance blockade to the effect of electron interference between two equivalent, strongly correlated, many-body states in the quantum dots. Finally, I will briefly review our very recent results of study of superconductor/semiconductor nanowire hybrid quantum structures.

20. (SEMINAR)"Magneto-transport Properties of Non-magnetic InGaAs Quantum Wells", Researcher Dr. Ning Dai (Shanghai Institute of Technical Physics), at 4:00 pm, October 26, 2010.

1. Abstract:
   The transport properties of a spin-split 2D electron gas system in an In0.53Ga0.47As/InP quantum well structure show interesting spin-related dynamics, even though only one electronic subband is occupied. An analytical method is developed to extract the quantum mobilities for the two spin subbands. Ionized impurity scattering and alloy disorder scattering are found to be the dominant mechanisms in this system. A larger quantum mobility is found for the higher-energy spin subband and the difference between the quantum mobilities for the two spin subbands can be tuned with the gate voltage. There exists a strong spin-orbit interaction in the 2D electron gas in the gated high-mobility In0.53Ga0.47As/InP quantum well. It is establish that the spin-orbit interaction is dominated by Rashba mechanism. Rashba spin-orbit coupling parameters determined from both the weak anti-localization and the beating pattern in Shubnikov-de Haas oscillations are in reasonable agreement with those derived from a simple kƒ8¥6p model. The zero-field spin splitting deduced from experiment shows non-monotonic behavior with a maximum as the electron density is varied by the applied gate voltage, which is satisfactorily explained within the Rashba model.

21. (SEMINAR)"Photonics with resonantly absorbing waveguide array", Prof. Dr. Jian-Ying Zhou (Sun Yat-sen University), at 4:00 pm, October 28, 2010.

1. Abstract:
   A waveguide array consisting of resonantly absorbing molecules presents a number of distinct characters over conventional waveguide array structures. An overview on the theoretical and experimental aspects of the imaginary photonic lattice, including incoherent and coherent control of optics fields, is first presented. Our experimental effort to fabricate the lattice is described. The functionality of the photonic structure is demonstrated with optical switching and optical buffering. Future effort for the real world application of the resonantly absorbing/amplifying waveguide array will be discussed.

22. (SEMINAR)"Spin relaxation in spin transport driven by electric field and temperature gradient", Asso. Prof. Dr. G. Tatara (Tokyo Metropolitan University, JAPAN) at 4:00 pm, November 1, 2010.

1. Abstract:
   Spin relaxation torque in the presence of the applied electric field and temperature gradient is theoretically studied . It is shown that the temperature gradient works on the spin transport as an effective electric field, just as the case of charge transport. The relaxation is shown to occur when the applied electric field or the temperature gradient has discontinuity. The results justify the phenomenological transport equation based on the spin chemical potential.

23. (SEMINAR)"Electric and Magnetic Resonances in Nanostructured Metamaterials", Prof. Dr. Ruwen Peng( Nanjing University) at 4:00 pm, December 21, 2010.

1. Abstract:
   In this talk, I discuss electric and magnetic resonances in a few stacks of nanostructured metamaterials. Firstly, I present the optical transmission through subwavelength nanoaperture arrays with periodic and fractal-like configurations, respectively, where both propagating surface plasmons and localized surface plasmons are excited and interfere with each other. In the second, I present that in an assembly of stacked metallic U-shaped resonators, pure magnetic and electric responses are respectively realized, and the magnetic and electric responses can be switched at the same frequency by changing the polarization of incident light. Thirdly, plasmonic antenna arrays and plasmonic waveguides are also discussed. The investigations provide flexibility in engineering surface-wave-based devices.