Vertex corrections to the anomalous Hall effect in spin-polarized two-dimensional electron gases with a Rashba spin-orbit interaction

We study the effect of disorder on the intrinsic anomalous Hall conductivity in a magnetic two-dimensional electron gas with a Rashba-type spin-orbit interaction. We find that anomalous Hall conductivity vanishes unless the lifetime is spin-dependent, similar to the spin Hall conductivity in the nonmagnetic system. In addition, we find that the spin Hall conductivity does not vanish in the presence of magnetic scatterers.     

Voltage-controllable spin-polarized transport through parallel-coupled double quantum dots with Rashba spin-orbit interaction

A spin device, consisting of parallel-coupled double quantum dots and three normal metal leads, is proposed to realize spin-polarized current without the help of magnetic field and magnetic material. Based on the Keldysh nonequilibrium Green function technique and equation of motion method, the spin-dependent current formula in each lead is derived. It is shown that not only a fully polarized current but also a tunable pure spin current can be obtained by modulating the structure parameters, strength of Rashba spin-orbit interaction and bias voltages properly. It further demonstrates the dependence of the spin-polarized current on the strength of the Rashba spin-orbit interaction.     

Universal spin-induced time reversal symmetry breaking in two-dimensional electron gases with Rashba spin-orbit interaction

We have experimentally studied the spin-induced time reversal symmetry (TRS) breaking as a function of the relative strength of the Zeeman energy (E(Z)) and the Rashba spin-orbit interaction energy (E(SOI)), in InGaAs-based 2D electron gases. We find that the TRS breaking, and hence the associated dephasing time tau(phi)(B), saturates when E(Z) becomes comparable to E(SOI). Moreover, we show that the spin-induced TRS breaking mechanism is a universal function of the ratio E(Z)/E(SOI), within the experimental accuracy.     

Rashba spin-orbit interaction and shot noise for spin-polarized and entangled electrons

We study shot noise for spin-polarized currents and entangled electron pairs in a four-probe (beam-splitter) geometry with a local Rashba spin-orbit (s-o) interaction in the incoming leads. Within the scattering formalism we find that shot noise exhibits Rashba-induced oscillations with continuous bunching and antibunching. We show that entangled states and triplet states can be identified via their Rashba phase in noise measurements. For two-channel leads, we find an additional spin rotation due to s-o induced interband coupling which enhances spin control. We show that the s-o interaction deter-mines the Fano factor, which provides a direct way to measure the Rashba coupling constant via noise.     

Anomalous Hall effect in a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction

We discuss the mechanism of the anomalous Hall effect in a Rashba-Dresselhaus two-dimensional electron gas subjected to a homogeneous out-of-plane magnetization. On the basis of a systematic treatment of the kinetic equations for the spin-density matrix, results are derived for the dynamic Hall conductivity in a closed form. Its nonanalytic dependence on both the scattering time and the frequency of the applied electric field is discussed. Except for in a special Rashba-Dresselhaus model, there is a finite intrinsic anomalous Hall effect, which is extremely sensitive to short-range elastic scattering.     

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.     

Thermoelectric effects in a double-dot Aharonov-Bohm interferometer with Rashba spin-orbit interaction

We investigate the thermoelectric effects in a double-dot Aharonov-Bohm interferometer coupled to ferromagnetic leads held at different temperatures. The interplay of Rashba spin-orbit interaction (RSOI) and magnetic flux ϕ induces various interesting spin-dependent interference phenomena. The thermoelectric transport oscillates with ϕ. The peak of the thermopower S and figure of merit ZT splits into two new peaks and its splitting increases with the Rashba induced phase factor φ _R . With increasing φ _R S and ZT at ϕ = ± 2nπ (n = 0,1,2,...) exhibit a conversion from a peak to a valley. In the presence of the interplay of RSOI and ϕ by increasing spin polarization the splitting peaks of S (ZT) become asymmetric and ZT is greatly enhanced. The influence of the quantum dot levels on thermoelectric effects is also analyzed.     

Spin filtering in a nonuniform quantum wire with Rashba spin-orbit interaction

We investigate theoretically the spin-polarized electron transport for a wide-narrow-wide (WNW) quantum wire under the modulation of Rashba spin-orbit interaction (SOI). The influence of both the structure of the quantum wire and the interference between different pairs of subbands on the spin-polarized electron transport is taken into account simultaneously via the spin-resolved lattice Green function method. It is found that a very large vertical spin-polarized current can be generated by the SOI-induced effective magnetic field at the structure-induced Fano resonance even in the presence of strong disorder. Furthermore, the magnitude of the spin polarization can be tuned by the Rashba SOI strength and structural parameters. Those results may provide an effective way to design a spin filter device without containing any magnetic materials or applying a magnetic field.     

Tunnel anisotropic magnetoresistance in graphene with Rashba spin-orbit interaction

Ballistic transport in a graphene-based normal/ferromagnetic barrier/normal junction in the presence of Rashba-type spin-orbit interaction (RSOI) is investigated by the non-equilibrium Green's function approach. It is found that due to the interplay between ferromagnetic exchange coupling and RSOI, the energy dispersion in the ferromagnetic barrier depends on the magnetization direction. The conductance changes by varying the magnetization direction, resulting in a tunnel anisotropic magnetoresistance (TAMR). The predicted TAMR effect oscillates with the RSOI strength or on-site energy, which is efficiently controllable by the gate voltage, making this junction very promising in spintronics applications.     

Rashba spin-orbit interaction in graphene armchair nanoribbons

We study graphene nanoribbons (GNRs) with armchair edges in the presence of Rashba spin- orbit interactions (RSOI). We impose the boundary conditions on the tight binding Hamiltonians for bulk graphene with RSOI by means of a sine transform and study the influence of RSOI on the spectra and the spin polarization in detail. We derive the low energy approximation of the RSOI Hamiltonian for the zeroth and first order in momentum and test their ranges of validity. The choice of a basis appropriate for armchair boundaries is important in the case of mode-coupling effects and leads to results that are easy to work with.     

Transport in magnetic graphene superlattice with Rashba spin-orbit interaction

Based on the transfer-matrix method, we have investigated the spin-dependent transport properties of magnetic graphene superlattice in the presence of Rashba spin-orbit interaction (RSOI). It is shown that the angular range of the spin transmission probability through magnetic graphene superlattice can be efficiently controlled by the number of barriers. As the number of magnetic barriers increases, the angular range of the transmission through the magnetic superlattice decreases, the gaps in the transmission and conductivity versus energy become wider. It is also found that the spin conductivities oscillate with the Fermi energy and RSOI strength. Specifically, when a magnetic field is present, the spin polarisation can be observed, whereas for the RSOI alone it is zero. Application of such a phenomenon to design a spin polarised electron device based on the graphene material is anticipated.     

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.     

Optical properties of BiTeI semiconductor with a strong Rashba spin-orbit interaction

We have modeled the 4f ¹-5d ¹ absorption spectrum of a LiYF₄:Ce³⁺ crystal at zero temperature using a microscopic model of the electron-phonon interaction and the real spectrum of LiYF₄ lattice vibrations. Effects caused by mixing of the wave functions of different states of the 5d ¹ excited configuration of the Ce³⁺ ion, which is induced by the electron-phonon interaction, are considered based on the calculations of the second-, third-, and fourth-order exact moments of curvature of the spectrum envelope. We have shown that the large value of the splitting between the maxima of the bands in the absorption spectrum that correspond to transitions to the third and fourth 5d ¹ levels is a result of the nonadiabatic interaction of 5d electrons with lattice vibrations.     

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-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.     

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.     

Electrically controllable spin transport in bilayer graphene with Rashba spin-orbit interaction

We study the spin transport in bilayer graphene nanoribbons (BGNs) in the presence of Rashba spin-orbit interaction (SOI) and external gate voltages. It is found that the spin polarization can be significantly enhanced by the interlayer asymmetry or longitudinal mirror asymmetry produced by external gate voltages. Rashba SOI alone in BGNs can only generate current with spin polarization along the in-plane y direction, but the polarization components can be found along the x, y and z directions when a gate voltage is applied. High spin polarization with flexible orientation is obtained in the proposed device. Our findings shed new light on the generation of highly spin-polarized current in BGNs without external magnetic fields, which could have useful applications in spintronics device design.     

Rashba and Dresselhaus spin-orbit interaction in semiconductor quantum wells

We theoretically investigate the Rashba and Dresselhaus spin-orbit interaction in AlAs/GaAs/Al_0.3Ga_0.7As/AlAs step-quantum wells. The ratio of Rashba and Dresselhaus spin splitting can be effectively manipulated by the well width and step width in the absence of electric field and magnetic field. When the well width of the step-quantum well is wider than 10 nm, the total spin splitting, which contains the contribution of interface as well as linear and cubic Dresselhaus terms, is always the greatest when the width of GaAs layer equals to about 2 nm. When the well width is wider than 2 nm, two different step widths can meet the SU(2) symmetry conditions, the smaller one of them results in maximum spin relaxation time. We also predict the application of the step-quantum well in spintronic devices.     

Nonlinear optical conductivity of two-dimensional semiconductors with Rashba spin-orbit coupling in terahertz regime

We explain how specific dynamical properties give rise to the limit distribution of sums of deterministic variables at the transition to chaos via the period-doubling route. We study the sums of successive positions generated by an ensemble of initial conditions uniformly distributed in the entire phase space of a unimodal map as represented by the logistic map. We find that these sums acquire their salient, multiscale, features from the repellor preimage structure that dominates the dynamics toward the attractors along the period-doubling cascade. And we explain how these properties transmit from the sums to their distribution. Specifically, we show how the stationary distribution of sums of positions at the Feigebaum point is built up from those associated with the supercycle attractors forming a hierarchical structure with multifractal and discrete scale invariance properties.     

Spin-polarized transport in adiabatic quantum point contact with strong Rashba spin-orbit interaction

We first report 0.5(2e²/h) conductance quantization in adiabatic quantum point contacts (QPCs) fabricated at high In-content InGaAs/InAlAs single heterojunctions under no magnetic field. This quantization seems difficult to understand, since the spin one-dimensional (1D) subbands in the QPCs are generally degenerated when B=0. However, this observation is reproducible in various QPC samples with different dimensions but not likely so definite as the conductance quantization in usual QPCs. It is noted that this particular heterojunction 2DEG is found to have high electron mobility of <5×10⁵ cm²/Vs as well as very large Rashba spin-orbit (SO) coupling constant of <35×10⁻¹² eVm. So that, the QPCs realized here can be regarded as a kind of Tomonaga-Luttinger wire with an enhanced Rashba interaction. In such a case, a mode coupling between the Rashba splitting 1D subbands gives rise to a spin-polarized transport in each ±k direction. This theory could be the one plausible candidate to explain the 0.5(2e²/h) conductance quantization observed here in the adiabatic QPC. This finding would be developed to novel spin-filters or spin-directional coupler devices based on nonmagnetic semiconductors.