The nondissipative spin Hall current in a nonuniform Rashba effect system

The spin Hall current in a two-dimensional electron system with nonuniform Rashba spin–orbit interaction (SOI) is investigated by means of the lattice Green's function method. Large electric and spin Hall currents are produced by this nonuniform Rashba SOI, while the electric Hall current vanishes in the uniform Rashba SOI system. A nondissipative spin Hall current is also produced, without any longitudinal voltage bias, any external magnetic field and any special class of band insulators.     

Rashba spin–orbit effect on the magnetocapacitance of a 2DEG in a diluted magnetic semiconductor

We investigate the magnetocapacitance of the two-dimensional electron gas (2DEG) embedded in diluted magnetic semiconductors in the presence of Rashba spin–orbit interaction (SOI). We present calculations on the energy spectrum and density of states and show that the tunable spin–orbit coupling and the enhanced Zeeman splitting have a strong effect on the magnetocapacitance of the structure. In the presence of Rashba SOI, a typical beating pattern with well defined node-positions in the oscillating capacitance is observed. A simple relation that predicts the positions of nodes in the beating patterns is obtained. The interplay between the total Zeeman splitting (including the s–d exchange interaction) and the Rashba SOI is discussed.     

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.     

Ballistic spin interferometer based on the Rashba and Dresselhaus spin-orbit interactions

By using the Al'tshuler-Aronov-Spivak (AAS) model, we give the amplitude changing with Rashba spin-orbit interaction (SOI) and Dresselhaus SOI strength. In the first idea 1D square loop (SL), Rashba SOI acts on two sides while Dresselhaus SOI acts on the other two sides. In the second SL, we consume Rashba SOI and Dresselhaus SOI act on four sides simultaneously. This model can be replaced by another one that Rashba SOI and Dresselhaus SOI act on every side independently, and each side is twice long. We theoretically illustrate the influence of the Dresselhaus SOI on node position and number. To explain the “half oscillation” phenomenon found in experiment, we apply Dresselhaus SOI to the ideal 1D SL. The conclusion is that the Dresselhaus SOI has a strong effect on the emergence of “half oscillation”.     

Rashba spin–orbit effect on the magnetocapacitance of a 2DEG in a diluted magnetic semiconductor

We investigate the magnetocapacitance of the two-dimensional electron gas (2DEG) embedded in diluted magnetic semiconductors in the presence of Rashba spin–orbit interaction (SOI). We present calculations on the energy spectrum and density of states and show that the tunable spin–orbit coupling and the enhanced Zeeman splitting have a strong effect on the magnetocapacitance of the structure. In the presence of Rashba SOI, a typical beating pattern with well defined node-positions in the oscillating capacitance is observed. A simple relation that predicts the positions of nodes in the beating patterns is obtained. The interplay between the total Zeeman splitting (including the s–d exchange interaction) and the Rashba SOI is discussed.     

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.     

Zero-field spin splitting in a two-dimensional electron gas with the spin-orbit interaction revisited

We consider a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction (SOI) in the presence of a perpendicular magnetic field. We derive analytical expressions of the density of states (DOS) of a 2DEG with the Rashba SOI in the presence of a magnetic field by using the Green's function technique. The DOS allows us to obtain the analytical expressions of the magnetoconductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and give rise to the beating patterns in the amplitude of the Shubnikov-de Haas (SdH) oscillations. We find a simple equation which determines the zero-field spin splitting energy if the magnetic field corresponding to any beat node is known from the experiment. Our analytical results reproduce well the experimentally observed non-periodic beating patterns, number of oscillations between two successive nodes and the measured zero-field spin splitting energy.     

Influence of spin–orbit interaction,Zeeman effect and light polarisation on the electronic and optical properties of pseudo-elliptic quantum rings under magnetic field

ABSTRACT

We theoretically investigated the influences of the magnetic field and light polarisation on the electronic and optical properties of a GaAs/GaAlAs pseudo-elliptic quantum ring, modelled by an outer ellipsis and an inner circle, in the presence of the Rashba and Dresselhaus spin–orbit interactions and Zeeman effect. We show that Aharonov-Bohm oscillations of the energy spectrum are not affected by the presence of the Zeeman effect alone but, in the presence of Rashba and Dresselhaus spin–orbit couplings, the periodicity of certain levels becomes hardly definite. The Zeeman effect generally enhances/diminishes the separation levels produced by Rashba/Dresselhaus interactions (SOI) and when both types of SOI are considered, the effect depends on their relative strength. The magnetic field can trigger spin-flip for each type of spin–orbit interaction and Zeeman effect or their combination through anticrossings in the energy spectra. Our results reveal that the absorption spectra are very sensitive to the magnetic field and light polarisation. For all polarisations considered, the magnetic field increment leads to the redshift or blueshift of some particular peaks (an effect of this ring geometry) and a better separation of the peaks. The x-polarised light determines spectra with many small, but separated peaks while the circular polarised light leads to spectra with large peaks of high amplitude.     

Second harmonic generation in a disk shaped quantum dot in the presence of spin-orbit interaction

The second harmonic generation (SHG) coefficients for a disk shaped quantum dot (DSQD) in the magnetic field are studied in the presence of spin-orbit interactions (SOI). The spin-orbit terms we have used in our calculations are both Rashba and Dresselhaus. We have shown that the presence of SOI modifies the SHG terms. In addition, it has been shown that SOI coupling terms influence the spectrum of DSQD resulting in defined changes in the harmonic generation.     

Spin Nernst effect in the absence of a magnetic field

We study the spin Nernst effect of a mesoscopic four-terminal cross-bar device with the Rashba spin–orbit interaction (SOI) in the absence of a magnetic field. The interplay between the spin Nernst effect and the seebeck coefficient is investigated for a wide range of the Rashba SOI. When no peaks appeared in the seebeck coefficient, an oscillatory spin Nernst effect still occurs. In addition, the disorder effect on the spin Nernst effect is also studied. We find that the spin Nernst effect can be enhanced up to threefold by disorder. Besides, due to the interface effect, the counter propagating of the charge current to the direction of the temperature gradient is possible for a nonuniform system.     

Spin–orbit interaction effects on plasmons in double coupled quantum wires

We report on collective and single-particle excitations of quasi-one-dimensional (Q1D) electron gas, experiencing Rashba spin–orbit interaction (SOI), and embedded in semiconductor-based coupled symmetrical and asymmetrical biwires. We choose five different and most significant situations regarding the conditions of anisotropy and tunneling between the wires. As the Rashba SOI strength increases, we find extra undamped plasmon modes resulting from the SOI induced spin splitting of those modes appearing in the absence of SOI. We also find these modes remaining in the gap between the spin-down and spin-up SPE continua. We show similar effects occurring on the optical and acoustical plasmon modes; signatures of collective excitations appearing in biwires without tunneling. We find those plasmons related to the spin-down charge density fluctuations being of the most robust modes concerning the increase of the Rashba SOI strength.     

Electron g-factor in quantum wire in the presence of Rashba effect and magnetic field

In this paper, we study the electron effective Landé g-factor in the InAs quantum wire under an applied magnetic field and the Rashba effect. For this goal, we first present an analytic solution to one-particle Schrödinger equation in the presence of both magnetic field and spin-orbit interaction (SOI). Then, using the obtained energy levels, we study the electron effective Landé g-factor. It is found that: (i) The effective Landé g-factor decreases when magnetic field increases. (ii) By increasing the confinement length l₀, the electron g-factor decreases. (iii) By increasing the strength of SOI, the electron g-factor increases.     

Spin-filtering and charge- and spin-switching effects in a quantum wire with periodically attached stubs

Spin-dependent electron transport in a periodically stubbed quantum wire in the presence of Rashba spin-orbit interaction (SOI) is studied via the nonequilibrium Green’s function (GF) method combined with the Landauer-Büttiker formalism. By comparing with a straight Rashba quantum wire, the magnitude of spin conductance can be enhanced obviously. In addition, the charge and spin switching can also be found in the considered system. The mechanism of these transport properties is revealed by analyzing the total charge density and spin-polarized density distributions in the stubbed quantum wire. Furthermore, periodic spin-density islands with high polarization are also found inside the stubs, owing to the interaction between the charge density islands and the Rashba SOI-induced effective magnetic field. These interesting findings may be useful in further understanding of the transport properties of low-dimensional systems and in devising an all-electrical multifunctional spintronic device based on the proposed structure.     

Quantum phase transitions in mesoscopic Rashba rings

Novel quantum phases are found in the ground state of Rashba ring: the orbital magnetic phase (OMP), non-OMP, pseudo-OMP and quasi-OMP, which depend on the spin-orbit interaction (SOI) strength, electron number and ring size. We give the phase diagram and their quantum-phase-transition conditions.     

Electron-dephasing time in a two-dimensional spin-polarized system with Rashba spin-orbit interaction

We calculate the dephasing time tau(phi)(B) of an electron in a two-dimensional system with a Rashba spin-orbit interaction, spin-polarized by an arbitrarily large magnetic field parallel to the layer. tau(phi)(B) is estimated from the logarithmic corrections to the conductivity within a perturbative approach that assumes weak, isotropic disorder scattering. For any value of the magnetic field, the dephasing rate changes with respect to its unpolarized-state value by a universal function whose parameter is 2E(Z)/E(SOI) (E(Z) is the Zeeman energy, while E(SOI) is the spin-orbit interaction), confirming the experimental report published in Phys. Rev. Lett. 94, 186805 (2005). In the high-field limit, when 2E(Z) > E(SOI), the dephasing rate saturates and reaches asymptotically to a value equal to half the spin-relaxation rate.     

电磁波辐照下量子线的电子自旋极化输运性质

理论上研究Rashba自旋-轨道相互作(SOI)量子线在外电磁波辐照下的电子自旋极化输运性质.在自由电子模型下利用散射矩阵方法,发现当Rashba SOI较弱时,自旋极化率与外电磁场频率和电子入射能量无关,而当Rashba SOI较强时,自旋极化率则强烈依赖于外场频率和电子入射能量,其物理根源是Rashba SOI使子带混合引起的.此外,当电子的入射能量增加到打开另一通道阈值时,电子的透射率出现一个反常的台阶结构,这来源于电子与光子的非弹性散射而使电子在子带间的跃迁. 关键词： 量子线 电磁波 自旋极化输运 散射矩阵     

Absence of spontaneous magnetic order of lattice spins coupled to itinerant interacting electrons in one and two dimensions

We extend the Mermin-Wagner theorem to a system of lattice spins which are spin coupled to itinerant and interacting charge carriers. We use the Bogoliubov inequality to rigorously prove that neither (anti-) ferromagnetic nor helical long-range order is possible in one and two dimensions at any finite temperature. Our proof applies to a wide class of models including any form of electron-electron and single-electron interactions that are independent of spin. In the presence of Rashba or Dresselhaus spin-orbit interactions (SOI) magnetic order is not excluded and intimately connected to equilibrium spin currents. However, in the special case when Rashba and Dresselhaus SOIs are tuned to be equal, magnetic order is excluded again. This opens up a new possibility to control magnetism electrically.     

Sum frequency generation in the spherical quantum dots in the presence of applied electric field and spin–orbit interaction

The sum-frequency generation (SFG) is theoretically studied in a quantum dot (QD) through the framework of the effective-mass approximation and compact density matrix approach. QD is spherical with the parabolic potential confinement, under applied electric field and in the presence of Rashba spin-orbit interaction (SOI). Using the computed energies and eigenkets, the second-order susceptibility of SFG has been also calculated as a function of radius of QD, spin–orbit interaction strength and the applied electric field. The effects of Rashba SOI strength, radius of QD and the applied electric field on the second-order of susceptibility coefficient are considered.     

Analytical base–collector depletion capacitance in vertical SiGe heterojunction bipolar transistors fabricated on CMOS-compatible silicon on insulator

The base--collector depletion capacitance for vertical SiGe npn heterojunction bipolar transistors (HBTs) on silicon on insulator (SOI) is split into vertical and lateral parts. This paper proposes a novel analytical depletion capacitance model of this structure for the first time. A large discrepancy is predicted when the present model is compared with the conventional depletion model, and it is shown that the capacitance decreases with the increase of the reverse collector--base bias--and shows a kink as the reverse collector--base bias reaches the effective vertical punch-through voltage while the voltage differs with the collector doping concentrations, which is consistent with measurement results. The model can be employed for a fast evaluation of the depletion capacitance of an SOI SiGe HBT and has useful applications on the design and simulation of high performance SiGe circuits and devices.     

Effects of multi-band mixing on the spin-polarized transport in quasi-one-dimensional electron waveguides

We present numerical calculations of the energy dispersion of spin-polarized electrons in quasi-one-dimensional electronic waveguides in the presence of Rashba spin–orbit interaction (SOI), by using an efficient expanded basis method. Within this model, the general mixing between any two subbands is taken into account. We investigate the properties of spin-polarized transport in the nonuniform SOI system. It is found that the multi-band mixing brings significant effects on the properties of multiple subbands transport in the regime of high energy, especially for the cases of the wide waveguide, the strong SOI and the long extension of the SOI region.