Rashba Spin-orbit Interaction Strength Research Articles

Quantum interference through parallel-coupled double quantum dots with Rashba spin-orbit interaction

The electronic transport through parallel-coupled double quantum dots with Rashba spin-orbit interaction is studied theoretically in the framework of the equation of motion of Green's function. Based on molecular state representation, the Fano interference in the conductance spectrum is readily explained. The possibility of manipulation of the Fano line shape of each spin component is explored by adjusting the Rashba spin-orbit interaction strength. It is also shown that the conductance of each spin component versus ϕ R exhibits a periodic function with the period of 4π. The Fano resonance retains even though the intradot Coulomb interaction is considered.

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.

Electrical manipulation of spins in the Rashba two dimensional electron gas systems

We present our theoretical and experimental studies on manipulation of electron spins based on the Rashba spin-orbit interaction (SOI) in semiconductor heterostructures. Quantum well (QW) thickness dependence of the Rashba SOI strength α is investigated in InP/InGaAs/InAlAs asymmetric QWs by analyzing weak antilocalization. Two different QW thicknesses show inverse Ns dependence of |α| in the same heterostructures. This inverse Ns dependence of |α| is explained by the k⋅p perturbation theory. We confirm that narrow wires are effective to suppress the spin relaxation. Spin interference effects due to spin precession are experimentally studied in small array of mesoscopic InGaAs rings. This is an experimental demonstration of a time reversal Aharonov–Casher effect, which shows that the spin precession angle in an InGaAs channel can be controlled by an electrostatic gate.

SPIN-RELATED TRANSPORT AFFECTED BY COMPETITION BETWEEN SPIN-ORBIT INTERACTION AND ZEEMAN EFFECT

The spin dynamics in solid state systems is governed by the competition between spin-orbit interaction (SOI) and the Zeeman effect. The SOI couples orbital motion of electron spins with an electric field. The Zeeman effect lifts the spin degeneracy in a magnetic field. In InGaAs -based 2DEGs, it is known that the Rashba SOI energy E SOI can be controlled by an electric field applied on the gate electrode.1 In the presence of SOI, weak localization (WL) due to time reversal symmetric interference changes to weak anti-localization (WAL). We have found crossover from WL to WAL by applying the gate voltage in InGaAs 2DEGs. Applying an in-plane magnetic field to the 2DEG does not affect the orbital motion of the electrons, but only modifies the Zeeman spin splitting energy E Z . This allows tuning the ratio between E SOI and E Z very accurately. We have studied how the interplay between SOI and Zeeman coupling affects the electron transport and the spin dynamics in InGaAs -based 2DEGs. From the quantitative analysis of the magnetoconductance, measured in the presence of an in-plane magnetic field, we conclude that this interplay results in a spin-induced breaking of time reversal symmetry (TRS) and in an enhancement of the spin relaxation time. Both effects are due to a partial alignment of the electron spin along the applied magnetic field, and are found to be in excellent agreement with recent theoretical predictions.2 We find that the electron dephasing time saturates when E Z becomes comparable to E SOI . Moreover, we show that the spin-induced electron dephasing time is a universal function of the ratio E Z /E SOI within the experimental accuracy, i.e. it is independent of any details of the quantum well.3 This universal behavior is explained by the recent theory.4 The suppression of WAL is observed by applying in-plane magnetic field because of the enhancement of the spin relaxation time, and this suppression also appears in narrow InGaAs wires since the effective magnetic field direction is confined by wires. In gate fitted narrow wires, the large enhancement of spin relaxation time is obtained when the Rashba SOI is decreased. The spin relaxation time is more than one order longer than that of 2DEG case. This enhancement suggests that the Rashba SOI strength approaches the Dresselhaus SOI strength. We have numerically investigated the angular dependence of in-plane magnetoconductance in disordered wires with both Rashba and Dresselhaus SOIs. A new method is proposed to determine the relative strength of Rashba and Dresselhaus SOI from transport measurements without the need of fitting parameters.5 This in-plane magnetic field measurement provides fruitful information on spin related transport. Note from Publisher: This article contains the abstract only.

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.

Effect of an in-plane magnetic field on the spin transport through a Rashba superlattice

We investigate spin-dependent transport properties of a single-channel planar electron waveguide under a periodic modulation of Rashba spin-orbit interaction (SOI) and subject to a weak in-plane magnetic field ${\mathbf{B}}_{\text{in}}$. The spatially periodic variation in the Rashba SOI strength gives rise to a band structure with full band gaps. The inclusion of ${\mathbf{B}}_{\text{in}}$ with a proper orientation angle $\ensuremath{\theta}$ (relative to the transport direction) introduces local band gaps where only two propagating (one right going and one left going) modes exist. As a result, for a finite superlattice with a sufficient number of periodic units, the generated spin polarization and its direction depend strongly on $\ensuremath{\theta}$. For a given Fermi energy higher than the Zeeman potential, there may exist several intervals of $\ensuremath{\theta}$ within which an optimal spin polarization is achieved.

All-Electrical Detection of the Relative Strength of Rashba and Dresselhaus Spin-Orbit Interaction in Quantum Wires

We propose a method to determine the relative strength of Rashba and Dresselhaus spin-orbit interaction from transport measurements without the need of fitting parameters. To this end, we make use of the conductance anisotropy in narrow quantum wires with respect to the directions of an in-plane magnetic field, the quantum wire, and the crystal orientation. We support our proposal by numerical calculations of the conductance of quantum wires based on the Landauer formalism which show the applicability of the method to a wide range of parameters.

Rashba spin-orbit interaction induced spin-polarized Andreev-reflection current through a double Aharonov–Bohm interferometer

Using the standard nonequilibrium Green’s function techniques, we investigate the spin-polarization dependent Andreev-reflection currents through a double Aharonov–Bohm interferometer with Rashba spin-orbit interaction. It is demonstrated that the spin polarization is induced by the Rashba spin-orbit interaction, which results in a phase difference between two quantum dots of the interferometer. The spin polarization of currents can be adjusted by tuning the Rashba spin-orbit interaction strength, the magnetic flux, and the interdot coupling as well, which lead to the transport current of complete spin polarization (either spin up or down) in both cases, with or without the interdot coupling. However, the current of complete spin polarization can approach its maximum value only in the absence of the interdot coupling.

Spin separation via a three-terminal Aharonov–Bohm interferometers

We propose a three-terminal ring-type device which contains a single-level quantum dot (QD) to extract or separate the spin-up and the spin-down electrons that are injected into the QD from a middle lead, into the left and the right leads, respectively. This scheme is based on the Rashba spin-orbit interaction (RSOI) in the bridge between the left and the right leads and is free from magnetic field or magnetic material. We find that both the spin directions and the magnitude of the outflow currents in the left and the right leads can be tuned by the RSOI strength and the structure parameters.

Pure spin current in a three-terminal spin device in the presence of Rashba spin-orbit interaction

The authors propose a spin device with three normal metal leads via a quantum dot in the presence of Rashba spin-orbit interaction, which operates independently on a magnetic field or ferromagnetic metals. It is shown that a pure spin current or a fully spin-polarized current can be obtained by modulating one of the voltages applied to three terminals. It further demonstrates the dependence of the pure spin current on the strength of Rashba spin-orbit interaction and the configuration of the three leads.

Charge-density and spin-density excitations in a two-dimensional electron gas with Rashba spin-orbit coupling

We study theoretically the charge-density and spin-density excitations in a two-dimensional electron gas in the presence of a perpendicular magnetic field and a Rashba type spin-orbit coupling. The dispersion and the corresponding intensity of excitations in the vicinity of cyclotron resonance frequency are calculated within the framework of random phase approximation. The dependence of excitation dispersion on various system parameters, i.e., the Rashba spin-orbit interaction strength, the electron density, the Zeeman spin splitting, and the Coulomb interaction strength is investigated.

COMBINED EFFECTS OF RASHBA SPIN-ORBIT INTERACTION STRENGTH AND ITS EXTENDED LENGTH IN QUANTUM WIRES

The combined effects of Rashba spin-orbit interaction (SOI) strength and the length of SOI excited region, which can be controlled by the external gate voltage deposited on the heterostructure, and on the electron spin precession in quasi-one-dimensional quantum wires are investigated by evaluating the relative conductance change, i.e. the ratio of difference of the conductances of the spin-up and spin-down polarized electrons to the total conductance. It is found that for proper wire width, electron spin precession can be smoothly achieved by co-adjusting the SOI strength and the length of SOI excited region. However, for wide quantum wire and strong SOI, the electron spin precession is significantly reduced due to the appearance of inter-subband mixing.

Spin-polarization in a 3-terminal conductor induced by Rashba spin–orbit coupling

We investigate numerically the spin polarization of the current in the presence of Rashba spin–orbit interaction (RSOI) in a 3-terminal conductor. We use equation-of-motion method to simulate the time evolution of the wave packet and focus on single-channel transport. A T-shaped conductor with uniform RSOI proposed by Kiselev and Kim and a Y-shaped conductor with nonuniform RSOI are considered. In the T-shaped conductor, the strength of RSOI is assumed to be uniform. We have found that the spin polarization becomes nearly 100% with little loss of conductance for sufficiently strong spin–orbit coupling. This is due to the spin-dependent group velocity of electrons at the junction which causes the spin separation. In the Y-shaped conductor, the strength of RSOI is modulated perpendicular to the charge current. A spatial gradient of effective magnetic field due to the nonuniform RSOI causes the Stern–Gerlach type spin separation. The direction of the polarization is perpendicular to the current and parallel to the spatial gradient. Again almost 100% spin polarization can be realized by this spin separation.

Effects of spin-orbit interaction and magnetic field on the electron transport in quasi-1D ferromagnetic/semiconductor/ferromagnetic system

Based on the transfer matrix method, we investigate the effects of Rashba spin-orbit interaction and magnetic field on the electron transport in a quasi one-dimensional FM/S/FM system, where FM and S represent the ferromagnetic metal and semiconductor, respectively. The results show that the oscillating scope of the transmission increases with the magnetic field increasing. In the antiferromagnetic alignment, the spin-up and spin-down electrons make the same contribution to the transmission even if a magnetic field is applied. In the ferromagnetic alignment, however, at certain strengths of Rashba spin-orbit interaction and of magnetic field, the transmission coefficient for spin-up electrons is larger than that for spin-down electrons, and the sign of the spin polarization changes, which is opposite to that in the absence of the magnetic field.