Inelastic light scattering by a two-dimensional electron system with Rashba spin-orbit coupling

Inelastic light scattering by a two-dimensional system of electrons in a conduction band with Rashba spinorbit coupling is studied theoretically for the resonance case where the frequencies of the incident and scattered light are close to the effective distance between the conduction band and spin-split band in a III–V semiconductor. It is shown that, in contrast to the case of no spin-orbit coupling, the spectrum of the scattered light exhibits a plasmon peak even for strictly perpendicular polarizations of the incident and scattered light. There exists a configuration where the scattering spectrum exhibits features originating from single-particle transitions only. Furthermore, it is shown that, for the general case of elliptic polarizations of the incident and scattered light, the amplitude of the plasmon peak depends on the sign of the effective Rashba spinorbit coupling constant and the signs of the phases of the polarization vectors. This fact can be used to determine the sign of the Rashba constant.     

Andreev reflection at the edge of a two-dimensional electron system with strong spin-orbit coupling

We experimentally investigate transport properties of a single planar junction between the niobium superconductor and the edge of a two-dimensional electron system in a narrow In_0.75Ga_0.25As quantum well with strong Rashba-type spin-orbit coupling. We experimentally demonstrate suppression of Andreev reflection at low biases at ultralow temperatures. From the analysis of temperature and magnetic field behavior, we interpret the observed suppression as a result of a spin-orbit coupling. There is also an experimental sign of the topological superconductivity realization in the present structure.     

Oscillations of the kinetic coefficients in a two-dimensional electron system with the spin-orbit interaction in an alternating magnetic field

The response of a two-dimensional electron system with the spin-orbit interaction to a measuring direct-current electric field is investigated for the case in which the system is disturbed from the equilibrium by a microwave alternating magnetic field. Point nonmagnetic impurities are considered as scattering sources. It is demonstrated that the combined transitions occurring under the action of an alternating magnetic field lead to new oscillations of the diagonal components of the electrical conductivity tensor of the two-dimensional electron gas.     

Tunneling conductance of a two-dimensional electron gas with Dresselhaus spin-orbit coupling

We theoretically studied the spin-dependent charge transport in a two-dimensional electron gas with Dresselhaus spin-orbit coupling (DSOC) and metal junctions. It is shown that the DSOC energy can be directly measured from the tunneling conductance spectrum. We found that spin polarization of the conductance in the propagation direction can be obtained by injecting from the DSOC system. We also considered the effect of the interfacial scattering barrier (both spin-flip and non-spin-flip scattering) on the overall conductance and the spin polarization of the conductance. It is found that the increase of spin-flip scattering can enhance the conductance under certain conditions. Moreover, both types of scattering can increase the spin polarization below the branches crossing of the energy band.     

Quantum Hall effect in a two-dimensional electron gas with spin-orbit coupling in the field of a surface superlattice

The Hall conductance of a two-dimensional electronic system with Rashba spin-orbit coupling in the presence of an external periodic potential of a superlattice and a perpendicular magnetic field has been calculated. The calculations were performed for an electron gas with parameters typical both of a system with weak spin-orbit coupling (AlGaAs/GaAs) and a system with relatively strong Rashba coupling (InGaAs/InAs).     

Current-induced spin polarization in a spin-polarized two-dimensional electron gas with spin-orbit coupling

The current-induced spin polarization (CISP) is investigated in a combined Rashba-Dresselhaus spin-orbit-coupled two-dimensional electron gas, subjected to a homogeneous out-of-plane magnetization. It is found that, in addition to the usual collision-related in-plane parts of CISP, there are two impurity-density-free contributions, arising from intrinsic and disorder-mediated mechanisms. The intrinsic parts of spin polarization are related to the Berry curvature, analogous with the anomalous and spin Hall effects. For short-range collision, the disorder-mediated spin polarizations completely cancel the intrinsic ones and the total in-plane components of CISP equal those for systems without magnetization. However, for remote disorders, this cancellation does not occur and the total in-plane components of CISP strongly depend on the spin-orbit interaction coefficients and magnetization for both pure Rashba and combined Rashba-Dresselhaus models.     

Electron spin precession in two-dimensional electron gas with Rashba spin-orbit coupling

Using the time-dependent Schrödinger equation, we present the analytical result of the expectation value of spin injected into a two-dimensional electron gas with respect to an arbitrarily spin-polarized electron state and monitor the spin time-evolution. We demonstrate that the expectation value of spin operator Sx is the time-independent, and only the expectation values in the Sy-Sz plane are time-dependent. A detailed study of spin precession in the spin-valve and spin-transistor geometry is presented, in which the initial spin-polarized electron state point perpendicular and parallel to the current direction, respectively. We put forward the possible reason that the resistance change is independent of gate voltage in the spin-valve geometry. Furthermore, it has been shown that the effective magnetic field generated by the spin-orbit interaction is not same with the truly magnetic field. The main effect of the truly magnetic field is to align the spin along the field direction, but the effective magnetic field generated by the spin-orbit interaction does not.     

Spin current and polarization in impure two-dimensional electron systems with spin-orbit coupling

We derive the transport equations for two-dimensional electron systems with Rashba spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations, we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation and spin current in a finite-size sample for an arbitrary ratio between spin-orbit energy splitting Delta and elastic scattering rate tau(-1). We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.     

Light scattering by a 2D electron system with spin-orbit interaction in a strong magnetic field

We theoretically investigate light scattering by electrons of a 2D system in a strong magnetic field perpendicular to the plane of the system (the filling factor is smaller than two, i.e., only the states of the zeroth Landau level are filled). Analysis is carried out in the resonance approximation, in which the frequencies of the incident and scattered light are close to the effective separation between the conduction band and one of the branches of the valence band of the semiconductor. Spin splitting of the Landau level in the conduction band associated with Zeeman and the spin-orbit interactions is taken into account. The dynamic screening effects are considered in the random phase approximation (RPA).     

Spin-Hall effect in two-dimensional electron systems with Rashba spin-orbit coupling and disorder

Using the four-terminal Landauer-Bu ttiker formula and Green's function approach, we calculate numerically the spin-Hall conductance in a two-dimensional junction system with the Rashba spin-orbit (SO) coupling and disorder. We find that the spin-Hall conductance can be much greater or smaller than the universal value e/8pi, 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. Our numerical calculation reveals that a nonzero SO coupling can induce electron delocalization for disorder strength smaller than a critical value, and the nonvanishing spin-Hall effect appears mainly in the metallic regime.     

Photoconductivity of 2D electron systems in magnetic field

According to recent photoconductivity measurements in 2D electron semiconductor systems in magnetic fields normal to the 2D plane, the photoconductivity as a function of magnetic field exhibits oscillations in the region of fields much weaker than those necessary for the observation of the Shubnikov-de Haas effect. In this paper, the aforementioned oscillations are interpreted as a two-dimensional analogue of magnetophoton (phonon) oscillations studied in detail by different authors on 3D samples.     

Magnetoplasma oscillations of a two-dimensional electron system with spin-orbit interaction in a lateral superlattice

Low-frequency magnetoplasmon modes in a one-dimensional lateral superlattice with Rashba spin-orbit splitting are considered. Such modes correspond to oscillations related to virtual transitions within a Landau level that become possible due to the broadening of each Landau level into a band produced by the superlattice potential. The specificity of the one-dimensional intersubband plasmons emerging in such a system has been revealed.     

Hopping transport in two-dimensional systems with spin-orbit interaction in external magnetic field

The theory of spin rotation waves (SRWs), representing excitations of a new type arising in twodimensional systems with spin-orbit interaction in an external electric field, has been developed. These intrinsic modes correspond to rotation of the magnetic moment vector in the plane formed by the electric field vector and the normal to the sample plate surface. An experimental method is proposed for detecting SRWs by measuring the frequency dependence of the magnetic susceptibility, which exhibits a resonance at the intrinsic mode frequency. A particular calculation is performed for a hopping conductivity model (for small-size polarons), but it is likely that intrinsic oscillations of the SRW type also take place for the band transport, since their appearance is related to the symmetry of the system.     

二维自旋轨道耦合电子气中持续自旋螺旋态的稳定性的研究

本文利用半经典的自旋密度矩阵方法对二维自旋轨道耦合电子气中持续自旋螺旋态的稳定性进行了一些研究, 重点研究了自旋螺旋态的寿命与其波矢、载流子迁移率、温度、自旋轨道耦合强度、外电场强度等因素之间的关系, 并将部分理论计算结果与最近的一些相关实验结果进行了比较,发现两者之间大致是符合的.     

Trapped two-dimensional condensates with synthetic spin-orbit coupling

We study trapped 2D atomic Bose-Einstein condensates with spin-independent interactions in the presence of an isotropic spin-orbit coupling, showing that a rich physics results from the nontrivial interplay between spin-orbit coupling, confinement and interatomic interactions. For low interactions two types of half-vortex solutions with different winding occur, whereas strong-enough repulsive interactions result in a stripe-phase similar to that predicted for homogeneous condensates. Intermediate interaction regimes are characterized for large enough spin-orbit coupling by an hexagonally-symmetric phase with a triangular lattice of density minima similar to that observed in rapidly rotating condensates.     

Anderson transition in two-dimensional systems with spin-orbit coupling

We report a numerical investigation of the Anderson transition in two-dimensional systems with spin-orbit coupling. An accurate estimate of the critical exponent nu for the divergence of the localization length in this universality class has to our knowledge not been reported in the literature. Here we analyze the SU(2) model. We find that for this model corrections to scaling due to irrelevant scaling variables may be neglected permitting an accurate estimate of the exponent nu=2.73+/-0.02.     

The recursion method for a two-dimensional electron system in a strong magnetic field

We study the tight-binding model of non-interacting electrons on a two-dimensional square lattice within a strong magnetic field. The recursion method is applied to this problem, and the asymptotic behaviour of the continued fraction coefficients and the appropriate termination of the continued fractions are discussed. For an ordered system the local density of states at bulk sites can efficiently and accurately be calculated. For any rational number =p/q of magnetic flux quanta per lattice site the spectral function is splitted in up toq different (Landau-like) subbands. At edge sites the gaps between the Landau subbands disappear. For a disordered system an appropriate termination of the continued fractions is more difficult. Nevertheless, reasonable results for the (bulk) density of states in the presence of disorder can be obtained by averaging over different system realizations. The corresponding result obtained within the coherent potential approximation (CPA) is in good agreement with the exact (averaged) density of states of the disordered system. It is shown that the broadening of each subband due to the disorder is considerably smaller than the disorder strength. The site off-diagonal matrix elements of the one-particle Green function can also be calculated and their unusual properties are discussed. Finally it is discussed, why a determination of the transport coefficients _xx and _xy from the Kubo formula was not yet possible within this method, not even within the CPA transport theory.     

太赫兹场辅助的单量子阱自旋共振输运

在考虑自旋轨道耦合的情况下,研究了通过一非磁性半导体异质结的太赫兹光子驱动的电子输运,研究结果显示频率相关的电导谱出现不对称的Fano型共振的劈裂;随着振荡场幅度的增加,多光子辅助过程出现;通过改变外加场参数,可以实现自旋过滤目的,特别是在干涉相消Fano型共振的频率位置时,出现了100%纯的自旋极化流.这些属性有助于大范围可调的自旋过滤器的实现并且可以得到纯的自旋透射流.