Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session U10: Focus Session: Spin Hall Effect |
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Sponsoring Units: DMP GMAG Chair: Igor Zutic, Naval Research Lab Room: LACC 153B |
Thursday, March 24, 2005 8:00AM - 8:12AM |
U10.00001: Spin current injection by intersubband transitions in quantum wells. Eugene Sherman, Ali Najmaie, John E. Sipe We show that a pure spin current can be injected in quantum wells by absorption of linearly polarized infrared radiation leading to transitions between subbands. The magnitude and the direction of the spin current depend on the Dresselhaus and Rashba spin-orbit coupling constants and light frequency and, therefore, can be manipulated by changing the light frequency and/or applying an external bias across the quantum well. The injected spin current should be observable either as a voltage generated via extrinsic spin-Hall effect, or by spatially resolved pump-probe optical spectroscopy. [Preview Abstract] |
Thursday, March 24, 2005 8:12AM - 8:24AM |
U10.00002: Electrical generation of spin in crystals with reduced symmetry Dimitrie Culcer, Yu Gui Yao, Allan MacDonald, Qian Niu We propose a way of generating a spin polarization in crystals with strong spin-orbit interactions. We show that, in the presence of an electric field, there exists an intrinsic torque term which gives rise to a nonzero spin generation rate. This spin generation rate is experimentally observable, as recent experimental progress in the detection of spin accumulation has shown. The wide applicability of this effect is emphasized by explicit consideration of a range of examples: bulk wurtzite and strained zincblende ($n$-GaAs) lattices, as well as quantum well heterojunction systems. [Preview Abstract] |
Thursday, March 24, 2005 8:24AM - 8:36AM |
U10.00003: Spin-Hall effect and related spin-charge transport in one and two- dimensional mesoscopic systems Ewelina Hankiewicz, Markus K\"onig, Laurens Molenkamp, Tomas Jungwirth, Jairo Sinova We study theoretically the spin transport and the spin Hall effect in one and two-dimensional mesoscopic systems with Rashba spin-orbit coupling. The non-equilibrium Green function formalism is used to model the samples with mobilities and Rashba coupling strengths experimentally available. In particular, we propose the realistic H-shape experimental setup where the indirect detection of spin-Hall effect is possible by measurement of voltage through paramagnetic contacts. We confirm the robustness of the intrinsic spin-Hall effect in mesosocopic systems against the disorder in agreement with the exact diagonalization and Born calculations in the bulk. Also, we discuss the influence of the effective Rashba and Zeeman fields on the spin and charge transport in mesoscopic structures of various shapes. Reference: Hankiewicz et al Phys. Rev. B Rapids (2004); cond-mat/0409334. [Preview Abstract] |
Thursday, March 24, 2005 8:36AM - 9:12AM |
U10.00004: Electrical Spin Generation and Transport in Spin-Orbit Coupled Systems Invited Speaker: Qian Niu We consider spin generation and transport in bands with built-in spin-orbit coupling. A number of fundamental issues will be discussed: (1) the existence of spin-dipole and torque-dipole of wave packets which model the carriers; (2) source terms in the continuity equation (spin generation and relaxation); (3) the composition of the spin current (Berry phase and more); (4) spin Hall conductivity and its reciprocal; (5) the spin current responsible for spin accumulation.\\[4pt] References:\\[0pt] [1] D. Culcer, J. Sinova, N. A. Sinitsyn, T. Jungwirth, A. H.MacDonald, Q. Niu, `Semiclassical theory of spin transport in spin-orbit coupled systems', Phys. Rev. Lett. 93, 046602 (2004).\\[0pt] [2] P. Zhang and Q. Niu, `Charge-Hall effect driven by spin force: reciprocal of the spin-Hall effect' Cond-mat/0406436.\\[0pt] [3] D. Culcer, Y. G. Yao, A. H. MacDonald, and Q. Niu, `Electric generation of spin in crystals with reduced symmetry', Cond-mat/0408020. [Preview Abstract] |
Thursday, March 24, 2005 9:12AM - 9:24AM |
U10.00005: Nonvanishing spin Hall Effect in a square-lattice system Shuichi Murakami Recently, it has been debated whether the spin Hall effect vanishes or not in the presence of impurities. To investigate this problem, we study a generic model on a square lattice with broken inversion symmetry, modelling a 2D semiconductor in a heterostructure. We adopt the Kubo formula and Keldysh formalism, assuming the clean limit from the disordered system. In the Keldysh formalism, the less Green function $G^{<}$ has two pieces contributing to the spin Hall effect. One is proportional to $n_{F}$ (contribution from the filled states) while the other is to $n'_{F}$ (contribution from the Fermi surface), where $n_{F}$ is the Fermi distribution. Both of these two pieces are intrinsic, as they are nonzero in the clean limit. In general models they do not cancel with each other. The Rashba model is exceptional as they cancel each other exactly by accident. We discuss a condition when the spin Hall effect becomes larger. In the spin Hall insulators, the spin Hall effect merely consists of the contribution from the filled states. [Preview Abstract] |
Thursday, March 24, 2005 9:24AM - 9:36AM |
U10.00006: Effect of electron correlations on the Spin-Hall conductivity in a 2D Rashba electron system S Satpathy, H Meskine The spin-Hall effect in 2D electron systems (2DES) is currently an intense field of theoretical research. In this work we study the spin-Hall effect in a two-dimensional electron system (2DES) with Rashba spin-orbit coupling and electron-electron Coulomb interaction. The problem is examined by performing a density-functional calculation of the 2DES and computing the conductivity $\sigma_{SH}$ using the Kubo-Greenwood formula. It is found that the Coulomb interaction renormalizes the spin-Hall conductivity and that the strength of the renormalization depends on the electron density $r_{s}$. [Preview Abstract] |
Thursday, March 24, 2005 9:36AM - 9:48AM |
U10.00007: Cancellation of intrinsic ``spin-Hall'' conductivity in absence of broken time-reversal symmetry Alexander Baytin, F.D.M. Haldane A Streda-type argument is used to obtain the intrinsic dissipationless ``spin-Hall'' conductivity of electronic systems with spin-orbit coupling (SOC). Instead of directly calculating the ``spin-current'' response to an electric field, we calculate the {\it spin-density} response to a magnetic flux density $B$ (from orbital, rather than Zeeman coupling), and transform to a moving frame in which an electric field is present. This is consistent when used to compute the ``anomalous'' and ``quantized'' (electrical) Hall conductivities, and appears to also be so for the ``spin-Hall'' conductivity: the induced ``spin-current'' in the moving frame is interpreted as the induced spin density in the static frame, times the boost velocity. In the 2D model with ``Rashba'' spin-orbit coupling, the spin density induced by linear response to $B$ is cancelled by an ``anomalous'' term from the lowest Landau level, which is ``special'' because it alone is spin-unpaired. Similar unpaired ``special'' Landau levels also occur in the 3D ``Luttinger'' model for SOC of holes in p-type semiconductors. We also argue that a {\it quantized} spin-Hall effect cannot occur in the absence of broken time-reversal symmetry, and conjecture that this is also true for the metallic (non-quantized) spin-Hall effect. [Preview Abstract] |
Thursday, March 24, 2005 9:48AM - 10:00AM |
U10.00008: Resonant manipulation of spin current with a double-barrier structure C. S. Chu, L. Y. Wang, C. S. Tang In this work, we consider a Rashba-type narrow channel consisting of two AC-biased finger-gates (FG) that orient perpendicularly and lie above the narrow channel. It is shown recently that such a gate configuration can give rise to dc spin current [1]. The dc spin current can be greatly enhanced by an optimal choice of the separation between the FGs. With the introduction of a double-barrier structure in between the FGs, we can explore the interplay between the dc spin current generation and the resonant levels in the double-barrier structure. Our results show that the direction of the dc spin current can be monitored by the chemical potential alone. No charge current, however, is generated in this configuration. [1] L. Y. Wang, C. S. Tang, and C. S. Chu, cond-mat/0409291 [Preview Abstract] |
Thursday, March 24, 2005 10:00AM - 10:12AM |
U10.00009: Spin-Hall Effect in Two-Diensional Spin-Orbit Coupled Systems with Disorder L. Sheng, D.N. Sheng, C.S. Ting The spin-Hall conductance of a two-dimensional electron system with the Rashba spin-orbit coupling and disorder is calculated numerically by using the Landauer-B\"{u}ttiker formula and Green's function approach. We find that the spin-Hall conductance can be much greater or smaller than the universal value $e/8\pi$, depending on the magnitude of the SO coupling, the electron Fermi energy and the disorder strength. The spin-Hall conductance does not vanish with increasing sample size for a wide range of disorder strength. The position-dependent spin polarization is also calculated. Our result is consistent with recent experimental observation of spin polarization near the edges of a semiconductor channel detected and imaged by using Kerr rotation microscopy. [Preview Abstract] |
Thursday, March 24, 2005 10:12AM - 10:24AM |
U10.00010: Maxwell Equation for the Coupled Spin-Charge Wave Propagation B. Andrei Bernevig, Xiaowei Yu, Shou-cheng Zhang We show that the dissipationless spin current in the ground state of the Rashba model gives rise to a reactive coupling between the spin and charge propagation, which is formally identical to the coupling between the electric and the magnetic fields in the $2+1$ dimensional Maxwell equation. This analogy leads to a remarkable prediction that a density packet can spontaneously split into two counter propagation packets, each carrying the opposite spins. In a certain parameter regime, the coupled spin and charge wave propagates like a transverse ``photon". We propose both optical and purely electronic experiments to detect this effect. [Preview Abstract] |
Thursday, March 24, 2005 10:24AM - 10:36AM |
U10.00011: Spin current corrleations induced by the Kondo effect Markus Kindermann Rapid technological progress over the past two decades has made available electrical conductors on the nanoscale. Due to their small size these conductors often have an effectively reduced dimensionality and one expects electron-electron interactions to play an important role. It is a fascinating but challenging endeavor to observe effects of these interactions in electrical measurements. Generically interactions manifest themselves in correlations. Measurements of current correlations should therefore most naturally be able to probe interactions. At low temperatures the Coulomb blockade in an interacting quantum dot is lifted by the Kondo effect. Although this effect results from interesting many-body correlations, no signatures of them have been found in previous calculations of current correlations. Since the Kondo effect results from spin fluctuations, one may expect it, however, to be observable in spin resolved transport measurements. I will show that this intuition is indeed correct. Kondo fluctuations can induce correlations between spin currents through a quantum dot. [Preview Abstract] |
Thursday, March 24, 2005 10:36AM - 10:48AM |
U10.00012: Topological Spin Current David Schmeltzer We show that the $SU(2)$ transformation which diagonalizes the two dimensional spin-orbit hamiltonian has a singularity in the momentum space at $\vec{K} = 0$ which gives rise to non-commuting cartesian coordinates. When an external electric field is applied, the non-commuting cartesian coordinates induce a Hall current. The presence of a random potential in an infinite system causes the single particle occupation at $\vec{K} = 0$ and the Hall current to vanishes. For a finite system, the spin-Hall conductance is quantized in units of $\frac{e g \mu_{B}}{2 h}$, and the charge-Hall conductivity increases with the strength of the Zeeman magnetic field. We propose an experiment to test our theory. [Preview Abstract] |
Thursday, March 24, 2005 10:48AM - 11:00AM |
U10.00013: Is The Intrinsic Spin Hall Effect Measurable? Zhaoyang Yang, Shufeng Zhang Despite of the large intrinsic spin Hall conductivity in a spin- orbit coupled material predicted theoretically, we show that the intrinsic spin Hall effect in any diffusive sample is not measurable via conventional transport methods, thus the research on the intrinsic spin Hall effect is limited at the pure theoretical content. After generally defining the intrinsic and extrinsic transport coefficients, we show that the intrinsic magnetization Hall current, which is the sum of the intrinsic spin and intrinsic orbit-angular-momentum Hall currents, is identically zero. More importantly, we demonstrate that the equation of motion for the spin density does not depend on the intrinsic spin Hall current, therefore the transverse spin accumulation is solely determined by the extrinsic spin Hall current. The zero intrinsic magnetization Hall current and the independence of the spin accumulation on the intrinsic spin Hall effect lead us to conclude that the intrinsic spin Hall effect can not be assessed by conventional spin transport experiments based on the measurement of the magnetization current and the spin accumulation at the edge of the sample. [Preview Abstract] |
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