Effect Of Rashba Spin-orbit Coupling Research Articles

Effect of Rashba spin-orbit coupling on the spin-dependent transport in magnetic tunnel junctions with semiconductor interlayers

Based on a mode match transfer matrix method and the quantum coherent transport theory of Mireles and Kirczenow, we investigate the coherent electron tunneling in FM/S1/I/S2/FM (FM represents the ferromagnetic metal layer, S1 and S2 represents the different semiconductor layer, respectively, I represents the insulator layer.) system. The effects of the thickness of the semiconductor layers and the Rashba spin-orbit coupling on the spin-dependent tunneling transmission coefficient and the properties of the tunnel magnetoresistance (TMR) are studied. It is found that the variations of tunneling transmission coefficients and the tunnel magnetoresistance TMR with Rashba spin-orbit coupling and the thickness of semiconductor layer, show typical resonant properties and the TMR can be enhanced and its sign can switch from positive to negative by increasing the ratio of Rashba spin-orbit coupling strength between two semiconductor layers.

Rashba spin–orbit coupling effect on a diluted magnetic semiconductor cylinder surface and ballistic transport

We have studied the Rashba spin–orbital effect on a diluted magnetic semiconductor (DMS) cylinder surface in the presence of a magnetic field parallel to the cylinder axis, taking into account the Zeeman coupling and the s–d exchange interaction between the carriers and the magnetic ions. We have obtained an analytical expression for the electron energy spectrum, which depends on the magnetic ion concentration, temperature and strength of magnetic field. The results are used to obtain the conductance of the cylinder at finite temperature. It is shown that the presence of additional local extremum points in the subbands of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential and magnetic field. In the presence of anomalous Zeeman terms with taking into account the Rashba splitting, each minimum of subband contributes G 0 / 2 to conductance and each local maxima in the subband, actually reduce the conductance by G 0 / 2 compared with the value G 0 , without the anomalous Zeeman splitting. The effect of finite temperature on the DMS cylinder conductance is a smearing out the sharp steps in the zero-temperature conductance, and shifting the peaks due to the temperature dependence of the s–d exchange interaction term.

Binding Energy and Spin-Orbit Splitting of a Hydrogenic Donor Impurity in AlGaN/GaN Triangle-Shaped Potential Quantum Well

In the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling, the binding energyEband spin-orbit split energy Г of the ground state of a hydrogenic donor impurity in AlGaN/GaN triangle-shaped potential heterointerface are calculated. We find that with the electric field of the heterojunction increasing, (1) the effective width of quantum well decreases and (2) the binding energy increases monotonously, and in the mean time, (3) the spin-orbit split energy Г decreases drastically. (4) The maximum of Г is 1.22 meV when the electric field of heterointerface is 1 MV/cm.

Selective suppression of Dresselhaus or Rashba spin-orbit coupling effects by the Zeeman interaction in quantum dots

We study single- and two-electron parabolic quantum dots in the presence of linear Dresselhaus and Rashba spin-orbit interactions. Contributions of both types of spin-orbit coupling are investigated in the context of the spin polarization of the system at high magnetic fields. We demonstrate that for negative Land\'e factors the effect of the Dresselhaus coupling is suppressed at high magnetic field, which for structures without inversion asymmetry leads to a completely spin-polarized system and a strict antisymmetry of the wave functions with respect to the interchange of spatial-electron coordinates. For negative Land\'e factor the Rashba coupling is preserved at high field and consequently the spin polarization of the systems as well as the spatial antisymmetry of the two-electron wave function remain approximate.

Transport and thermodynamic properties of a 2DEG in the presence of tilted magnetic field: the influence of Rashba interaction

The effects of Rashba spin-orbit coupling on the physical properties of a non-interacting two-dimensional electron gas (2DEG) in presence of a tilted magnetic field are investigated. The spin-orbit and Zeeman interactions depend on the intensity and direction of the external magnetic field and we study their influence on the physical properties of the system. We obtain the energy spectrum, the density of states, the Fermi energy, and we analyze the combined effect of the Zeeman and Rashba Spin-Orbit Interaction on the transport and thermodynamic properties.

Influence of the illumination on weak antilocalization in an AlxGa1−xN∕GaN heterostructure with strong spin-orbit coupling

The weak antilocalization effects of the two-dimensional electron gas in a high mobility AlxGa1−xN∕GaN heterostructure have been investigated by means of magnetotransport measurements before and after illumination. The zero-field spin splitting mainly arising from the Rashba spin-orbit coupling effect as a function of electron concentration as well as a function of temperature is studied using the weak antilocalization analysis. The Rashba spin-orbit coupling constant α deduced using the weak antilocalization analysis shows a rapid decrease with the increase of the measured electron concentration.

Weak antilocalization and beating pattern in high electron mobility AlxGa1−xN/GaN two-dimensional electron gas with strong Rashba spin-orbit coupling

The weak antilocalization (WAL) effects of the two-dimensional electron gas (2DEG) in high mobility AlxGa1−xN/GaN heterostructure as well as beating patterns in the Shubnikov–de Haas (SdH) oscillatory magnetoresistance have been investigated by means of magnetotransport measurements before and after illumination. The zero-field spin splitting mainly arising from the Rashba spin-orbit coupling effect is studied using the weak antilocalization and beating patterns analysis, respectively. The Rashba spin-orbit coupling constant α deduced using the weak antilocalization analysis showed a good agreement with that estimated from the analysis of the beating patterns for the sample before and after illumination. For our sample, the electron motion in the high mobility system is in the ballistic regime, the experimental WAL curves were fitted by a simulated quantum conductance correction according to a model proposed by [Golub [Phys. Rev. B 71, 235310 (2005)].

Rashba spin-orbit effect on the zero conductance and the magnetoresistance of a quantum ring

Using a mode matched scattering matrix method, we study the effect of Rashba spin-orbit coupling and a tunnel barrier on the zero conductance and the tunnel magnetoresistance (TMR) in a one-dimensional conducting Aharonov–Bohm ring symmetrically coupled to two ferromagnetic leads. It is found that the conductances of spin-up and spin-down electrons show periodic variations as the ring’s length changes. The conductance amplitude in antiferromagnetic alignment is very different from that in ferromagnetic alignment. The lifting of the real zero conductance is changed by the spin-orbit interaction and the tunnel barrier. The numerical results also show that this structure can provide a large TMR. When the ring’s length is increased, the TMR varies its period.

Spin-orbit splitting of a hydrogenic donor impurity in GaAs∕GaAlAs quantum wells

The electronic states of a hydrogenic donor impurity in GaAs∕GaAlAs quantum wells are investigated theoretically in the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling. The splits of electron energy levels are calculated. The results show that (1) the split energy of the excited state is larger than that of the ground state; (2) the split energy peak appears as the GaAs well width increases from zero; and (3) the maximum split energy reaches about 1.6meV. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices.

Spin-orbit coupling effect on persistent currents in a one-dimensional quantum ring with an Anderson impurity

Based on the finite $U$ slave boson method, we have investigated the effect of Rashba spin-orbit (SO) coupling on the persistent charge and spin currents in a one-dimensional quantum ring with a magnetic impurity. We have used a tight-binding model in the momentum space for electrons in the ring and the Anderson impurity model for the magnetic impurity. It is shown that the Kondo effect will decrease the magnitude and change the curve shape of the persistent charge and spin currents significantly in this side-coupled Anderson impurity case. In the presence of SO coupling, the persistent currents change drastically and show oscillations with the strength of SO coupling ${\ensuremath{\alpha}}_{R}$. The direction of the persistent current can be reversed by tuning ${\ensuremath{\alpha}}_{R}$. For the system with an odd number of electrons, there are abrupt jumps of the persistent currents at the position of level crossing. It is also found that a persistent spin current circulating the ring can exist even without the charge current in this system.

Combined effect of Rashba spin-orbit coupling and disorder on the symmetry of superconducting pairing

Based on Bogoliubov-de Gennes equation, we investigate the superconducting pairing due to the nearest-neighboring attractive interaction in the presence of the Rashba spin-orbit coupling (SOC). It is found that the superconducting is still of the singlet nature and dominated by the $d$-wave symmetry in the presence of SOC and in the absence of disorder. The pairing strength has decreasing maxima as the SOC strength increases due to its destructive effect on the superconductivity and shows a periodiclike oscillation reflecting the relationship between the characteristic length of SOC and the coherent length of superconductivity. In the presence of SOC and disorder, the pairing has both the singlet and triplet components, and the $s$- and $p$-wave symmetries are induced in addition to the dominant $d$-wave symmetry. The related strengths of different pairing components exhibit complicated dependence on the strengths of the SOC and the disorder.

Persistent spin and charge currents and magnification effects in open ring conductors subject to Rashba coupling

We analyze the effect of Rashba spin-orbit coupling and of a local tunnel barrier on the persistent spin and charge currents in a one-dimensional conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First, as an important consequence of the spin-splitting, it is found that a persistent spin current can be induced which is not simply proportional to the charge current. Second, a magnification effect of the persistent spin current is shown when one tunes the Fermi energy near the Fano-type antiresonances of the total transmission coefficient governed by the tunnel barrier strength. As an unambiguous signature of spin-orbit coupling we also show the possibility to produce a persistent pure spin current at the interference zeros of the transmittance. This widens the possibilities of employing mesoscopic conducting rings in phase-coherent spintronics applications.

Theory of tunneling conductance in normal metal/triplet superconductor junctions without inversion symmetry

We study tunneling conductance in normal metal/triplet superconductor junctions without inversion symmetry by solving the Bogoliubov–de Gennes equation. We consider a pairing symmetry, d ( k ) ∝ x ^ k y - y ^ k x . The effect of Rashba spin-orbit coupling (RSOC) is taken into account. We find that the RSOC induces a peak at the energy gap like s-wave superconductors in the tunneling spectrum. This is because the two of four eigenfunctions of the Hamiltonian for triplet pairing coincide with those for s-wave pairing when a relation holds between pairing symmetry and spin-orbit coupling, indicative of an s-wave-like property of triplet superconductors. As a result, the tunneling spectrum has s- and p-wave like features. This may serve as a tool for determining the pairing symmetry of triplet superconductors without inversion symmetry.

Zero-conductance resonances and spin filtering effects in ring conductors subject to Rashba coupling

We investigate the effect of Rashba spin-orbit coupling and of a tunnel barrier on the zero conduc- tance resonances appearing in a one-dimensional conducting Aharonov-Bohm (AB) ring symmet- rically coupled to two leads. The transmission function of the corresponding one-electron problem is derived within the scattering matrix approach and analyzed in the complex energy plane with focus on the role of the tunnel barrier strength on the zero-pole structure characteristic of trans- mission (anti)resonances. The lifting of the real conductance zeros is related to the breaking of the spin-reversal symmetry and time-reversal symmetry of Aharonov-Casher (AC)and AB rings, as well as to rotational symmetry breaking in presence of a tunnel barrier. We show that the polarization direction of transmitted electrons can be controlled via the tunnel barrier strength and discuss a novel spin-filtering design in one-dimensional rings with tunable spin-orbit interaction.

Two-dimensional S-N-S junction with Rashba spin-orbit coupling

The effect of Rashba spin-orbit coupling on the supercurrent in S-2DEG-S proximity junctions is investigated in the clean limit. A generalization of Beenakker’s formula for Andreev levels to the case of spin-orbit scattering is presented. Spin-orbit induced splitting of Andreev bound states is predicted for an infinite-width junction with nonvanishing normal backscattering at S-N interfaces. However, a semiclassical average of the Josephson current is insensitive to the Rashba coupling as long as the electron-electron interaction in 2DEG is neglected.

Intrinsicallys-wave-like property of triplet superconductors with spin-orbit coupling

We have studied a general property of unconventional superconductors (USs) with spin-orbit coupling by solving the Bogoliubov--de Gennes equation and found that the two of four eigenfunctions for triplet pairing coincide with those for $s$-wave pairing when a relation holds between pairing symmetry and spin-orbit coupling, indicative of an intrinsically $s$-wave-like property of triplet superconductors. Applying the result, we have studied the tunneling conductance in normal metal/insulator/unconventional superconductor junctions with a pairing symmetry $\mathbf{d}(\mathbf{k})\ensuremath{\propto}\stackrel{\mathrm{\ifmmode \hat{}\else \^{}\fi{}}}{\mathbf{x}}{k}_{y}\ensuremath{-}\stackrel{\mathrm{\ifmmode \hat{}\else \^{}\fi{}}}{\mathbf{y}}{k}_{x}$. The effect of Rashba spin-orbit coupling (RSOC) is taken into account. We have found that the RSOC induces a peak at the energy gap like $s$-wave superconductors in the tunneling spectrum, which stems from the intrinsically $s$-wave-like property of a triplet component of the US. As a result, the tunneling spectrum has $s$- and $p$-wave-like features. This may serve as a tool for determining the pairing symmetry of USs without inversion symmetry.

Spin-polarized transport in one-dimensional waveguide structures with spatially-periodic electronic and magnetic fields

We investigate theoretically the spin-polarized transport in one-dimensional waveguide structure with spatially-periodic electronic and magnetic fields. The interplay of the spin–orbit interaction and in-plane magnetic field significantly modifies the spin-dependent transmission and the spin polarization. The in-plane magnetic fields increase the strength of the Rashba spin–orbit coupling effect for the electric fields along y axis and decrease this effect for reversing the electric fields, even counteract the Rashba spin–orbit coupling effect. It is very interesting to find that we may deduce the strength of the Rashba effect through this phenomenon.

Rashba spin-orbit coupling effect on the noise in quasi-one-dimensional nanowires under an applied magnetic field

Using an adiabatic approximate method, the noise of quasi-one-dimensional nanowires modeled with a soft-wall potential is investigated at finite temperature in the presence of the Rashba spin-orbit interaction and magnetic and electric fields. In the presence of the Rashba spin-orbit interaction, spin-split subbands are shifted horizontally in the energy-wave-vector plane. As a result, the curves of the noise shift toward the left. The results also indicate that the noise is strongly spin dependent due to the spin split originating from the Zeeman effect. With increasing magnetic field and bias voltage, the quantum shot noise becomes dominant.

Rashba spin precession in quantum-Hall edge channels

Quasi-one-dimensional edge channels are formed at the boundary of a two-dimensional electron system subject to a strong perpendicular magnetic field. We consider the effect of Rashba spin-orbit coupling, induced by structural inversion asymmetry, on their electronic and transport properties. Both our analytical and numerical results show that spin-split quantum-Hall edge channels exhibit properties analogous to that of Rashba-split quantum wires. Suppressed backscattering and a long spin lifetime make these edge channels an ideal system for observing voltage-controlled spin precession. Based on the latter, we propose a magnetless spin-dependent electron interferometer.

Asymmetric effect on spin polarization in a spin-filter device using nonmagnetic triple-barrier structure

We investigate the asymmetric effect in a spin-filter device, which is based on the Rashba spin-orbit coupling effect and uses a nonmagnetic tunneling diode. The structural asymmetry is introduced by unequivalence of the two quantum wells in the spin-filter device. It is found that the structural asymmetry can greatly change spin-filtering efficiency. For some asymmetric spin-filter structures, one can see spin-dependent enhancement in the transmission. Moreover, the current density can increase or decrease greatly depending on the degree of the structural asymmetry.