Browsing by Author "Mal'shukov, A. G."

Now showing 1 - 11 of 11

Asymmetries in intrinsic spin-Hall effect in low in-plane magnetic field
(2008-10-01)
Wang, L. Y.
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Chu, C. S.
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Mal'shukov, A. G.
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電子物理學系
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Department of Electrophysics
Effects of low in-plane magnetic field on bulk spin densities and edge spin accumulations of a diffusive two-dimensional semiconductor stripe are studied. Focusing upon the Dresselhaus-type intrinsic spin-orbit interaction (SOI), we look for the symmetry, or asymmetry, characteristics in two magnetic-field orientations: along and transverse to the stripe. For longitudinal field, the out-of-plane spin density S(z) exhibits odd parity across the stripe and even parity in the magnetic field and is an edge accumulation. For transverse field, the out-of-plane S(z) becomes asymmetric in both spatial and field dependencies and has finite bulk values for finite magnetic fields. Our results support utilizing low in-plane magnetic fields for the probing of the underlying SOI.
Competing interplay between Rashba and cubic-k Dresselhaus spin-orbit interactions in spin-Hall effect
(2009-05-01)
Chang, R. S.
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Chu, C. S.
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Mal'shukov, A. G.
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電子物理學系
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Department of Electrophysics
Focusing on the interplay between the Rashba and cubic-k Dresselhaus spin-orbit interactions (SOI), we calculate the spin accumulation S-z and the spin polarizations S-i(B) at, respectively, the lateral edges and in the bulk of the two-dimensional electron gas. Their dependences on both the ratio between the Rashba and the Dresselhaus SOI coupling constants and the electron densities are studied systematically. Strong competition features in S-z are found. In the Dresselhaus-dominated regime S-z changes sign when the electron density is large enough. In the Rashba-dominated regime S-z is essentially suppressed. Most surprising is our finding that the Rashba-dominated regime occurs when alpha approximate to 2 beta, where alpha and beta are the Rashba and the effective linear-k Dresselhaus SOI coupling constants, respectively. For the spin polarizations S-i(B), the Rashba-dominated regime occurs when alpha >=beta. Our results point out that decreasing parallel to alpha parallel to leads to the restoration of the spin accumulation S-z.
Nonuniversality of the intrinsic inverse spin-Hall effect in diffusive systems
(2012-04-02)
Wang, L. Y.
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Mal'shukov, A. G.
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Chu, C. S.
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電子物理學系
;
Department of Electrophysics
We studied the electric current induced in a two-dimensional electron gas by the spin current, in the presence of Rashba and cubic Dresselhaus spin-orbit interactions. We found out that the factor relating the electric and spin currents is not universal, but rather depends on the origin of the spin current. Drastic distinction has been found between two cases: the spin current created by diffusion of an inhomogeneous spin density, and the pure homogeneous spin current. We found that in the former case the inverse spin-Hall effect electric current is finite, while it turns to zero in the latter case, if the spin-orbit coupling is represented by Rashba interaction.
Resonant spin dipole induced by an in-plane potential gradient spin-orbit interaction
(2007-10-01)
Chen, K. Y.
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Chu, C. S.
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Mal'shukov, A. G.
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電子物理學系
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Department of Electrophysics
Spin-orbit interaction (SOI) arising from in-plane potential gradient is invoked for the generation of spin accumulation in a driven electric field. The SOI and a local in-plane potential pattern together bring about resonant spin dependent scatterings to electrons in a nonequilibrium distribution. In the vicinity of a ring-shaped potential barrier pattern, a spin dipole distribution with a resonant dipole strength characteristic is obtained. As the chemical potential mu is increased across one such resonant energy, the dipole strength manifests both sign reversal and large amplitude enhancement. The scattering resonance, thus, provides an additional knob for the manipulation of the spin accumulation.
Semiclassical path integral approach for spin relaxations in narrow wires
(2009-03-01)
Chang, Cheng-Hung
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Tsai, Jengjan
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Lo, Hui-Fen
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Mal'shukov, A. G.
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數學建模與科學計算所(含中心)
The semiclassical path integral (SPI) method has been applied for studying spin relaxation in a narrow two-dimensional strip with the Rashba spin-orbit interaction. Our numerical calculations show good agreement with the experimental data, although some features of experimental results are not clear yet. We also calculated the relaxation of a uniform spin-density distribution in the ballistic regime of very narrow wires. With the decreasing wire width, the spin polarization exhibits a transition from the exponential decay to the oscillatory Bessel-type relaxation. The SPI method has also been employed to calculate the relaxation of the particularly long-lived helix mode. Good agreement has been found with calculations based on the diffusion theory.
Spin cloud induced around an elastic scatterer by the intrinsic spin Hall effect
(2006-08-18)
Mal'shukov, A. G.
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Chu, C. S.
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電子物理學系
;
Department of Electrophysics
Similar to the Landauer electric dipole created around an impurity by the electric current, a spin polarized cloud of electrons can be induced by the intrinsic spin Hall effect near a spin independent elastic scatterer. It is shown that in the ballistic range around the impurity, such a cloud appears in the case of Rashba spin-orbit interaction, even though the bulk spin Hall current is absent.
Spin generation in a Rashba-type diffusive electron system by nonuniform driving field
(2010-03-01)
Wang, L. Y.
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Chu, C. S.
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Mal'shukov, A. G.
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電子物理學系
;
Department of Electrophysics
We show that the Rashba spin-orbit interaction contributes to edge spin accumulation S(z) in a diffusive regime when the driving field is nonuniform. Specifically, we solve the case of nonuniform driving field in the vicinity of a circular void locating in a two-dimensional electron system and we identify the key physical process leading to the edge spin accumulation. The void has radius R(0) in the range of spin-relaxation length l(so) and is far from both source and drain electrodes. The key physical process we find is originated from the nonuniform in-plane spin polarizations. Their subsequent diffusive contribution to spin current provides the impetus for the edge spin accumulation S(z) at the void boundary. The edge spin accumulation is proportional to the Rashba coupling constant alpha and is in a spin-dipole form oriented transversely to the driving field. We expect similar spin accumulation to occur if the void is at the sample edge.
Spin Hall effect in a Josephson contact
(2008-09-01)
Mal'shukov, A. G.
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Chu, C. S.
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電子物理學系
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Department of Electrophysics
The spin Hall effect on the Josephson tunneling through a two-dimensional normal contact with a spin-orbit split conduction band has been studied in the diffusive regime and at the zero electric bias. Linearized Usadel equations for triplet components of the pairing function in the presence of intrinsic spin-orbit interaction have been derived. These equations have been employed for analysis of the spin Hall effect induced by the super-current. We predict that a nondissipative out-of-plane spin Hall polarization accumulates at lateral edges and an in-plane polarization is induced throughout the entire normal region. At the same time, in contrast to the spin Hall effect in normal systems, the spin current is absent in the considered case of the stationary Josephson effect.
Spin orientation and spin-Hall effect induced by tunneling electrons
(2007-12-01)
Mal'shukov, A. G.
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Chu, C. S.
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電子物理學系
;
Department of Electrophysics
It is shown that a flux of unpolarized electrons across a symmetric double barrier quantum well induces a spin polarization inside the well. Besides, the transmitted current acquires a spin polarized component and the spin-Hall current flows in the planar direction. These phenomena are due to a combined effect of Dresselhaus interaction and the spin-orbit interaction induced by gradients of heterostructure material parameters. In contrast to previous studies of the spin filtering effect, we predict that it can be observed in the case of an isotropic distribution of incident electrons.
Spin-Hall current and spin polarization in an electrically biased SNS Josephson junction
(2011-08-10)
Mal'shukov, A. G.
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Chu, C. S.
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電子物理學系
;
Department of Electrophysics
Periodic in time spin-Hall current and spin polarization induced by a dc electric bias have been calculated in a superconductor-normal two-dimensional electron gas-superconductor (SNS) Josephson junction. We assumed that the band energies of electrons in the normal system are split due to Rashba spin-orbit coupling. The transport parameters have been calculated within the diffusion approximation and by using perturbation expansion over a small SN contact transparency. We found out that, in contrast to the stationary Josephson effect, the spin-Hall current does not turn to zero. Besides a direct proximity effect caused by a Cooper pair's transition into a triplet state, the spin current and polarization are also driven by a periodic electric field associated with the charge imbalance.
Spin-Hall interface resistance in terms of Landauer-type spin dipoles
(2007-02-01)
Mal'shukov, A. G.
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Wang, L. Y.
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Chu, C. S.
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電子物理學系
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Department of Electrophysics
We considered the nonequilibrium spin dipoles induced around spin-independent elastic scatterers by the intrinsic spin-Hall effect associated with the Rashba spin-orbit coupling. The spin polarization normal to the two-dimensional electron gas (2DEG) has been calculated in the diffusion range around the scatterer. Although around each impurity this polarization is finite, we found that the corresponding macroscopic spin density obtained via averaging of individual spin dipole distributions over impurity positions is zero in the bulk. At the same time, the spin density is finite near the boundary of 2DEG, except for a special case of a hard wall boundary, that is, when it turns to 0. The boundary value of the spin polarization can be associated with the interface spin-Hall resistance determining the additional energy dissipation due to spin accumulation.