Influence of Rashba spin-orbit coupling on Josephson effect in triplet superconductor/two-dimensional semiconductor/triplet superconductor junctions

We study theoretically Josephson effect in a planar ballistic junction between two triplet superconductors with p-wave orbital symmetries and separated by a two-dimensional (2D) semiconductor channel with strong Rashba spin-orbit coupling. In triplet superconductors, three types of orbital symmetries are considered. We use Bogoliubov-de Gennes formalism to describe quasiparticle propagations through the junction and the supercurrents are calculated in terms of Andreev reflection coefficients. The features of the variation of the supercurrents with the change of the strength of Rashba spin-orbit coupling are investigated in some detail. It is found that for the three types of orbital symmetries considered, both the magnitudes of supercurrent and the current-phase relations can be manipulated effectively by tuning the strength of Rashba spin-orbit coupling. The interplay of Rashba spin-orbit coupling and Zeeman magnetic field on supercurrent is also investigated in some detail.     

Specular Andreev reflection in the interface of a two-dimensional semiconductor with Rashba spin-orbit coupling and a d-wave superconductor

We reveal that the recently discovered specular Andreev reflection (SAR) [C. W. J. Beenakker, Phys. Rev. Lett. 97, 067007 (2006)] can occur in semiconductors where the spin-orbit coupling is finite. We demonstrate this finding in the hybrid of a two-dimensional electron gas with Rashba spin-orbit coupling and a superconductor. In the limit of low density or a strong spin-orbit coupling, specular Andreev reflection is finite. We also show that unit electron-hole conversion is possible in a specular Andreev reflection due to the different topological structures of the equal-energy surface between electrons and holes. The SAR in the semiconductor is determined by the relative orientation of wave vector to group velocity, which can be analyzed by ray equations.     

Charge transport through ferromagnet/two-dimensional electron gas/d-wave superconductor junctions with Rashba spin-orbit coupling

Along the lines of Blonder, Tinkham and Klapwijk, we investigate the charge transport through ferromagnet/two-dimensional electronic gas/d-wave superconductor (F/2DEG/S) junctions in the presence of Rashba spin-orbit (SO) coupling and focus our attention on the interplay between spin polarization and spin precession. At zero spin polarization, the spin-mixing scattering resulted from Rashba SO coupling decreases the zero-bias conductance peak. Under spin polarization, spin precession introduces novel Andreev reflection, which competes with the effect of spin-mixing scattering. If the F layer is a half metal, the later effect is overwhelmed by that of novel Andreev reflection. As a result, the zero-bias conductance dip caused by spin polarization is enhanced, and at strong Rashba SO coupling, a split zero-bias peak is found in the gap. In an intermediate region where the two effects are comparable with each other, the zero-bias conductance shows a reentrant behavior as a function of Rashba SO coupling.     

Rashba spin-orbit effect on dwell time of electrons tunneling through semiconductor barrier

A study on characteristics of electrons tunneling through semiconductor barrier is evaluated, in which we take into account the effects of Rashba spin-orbit interaction. Our numerical results show that Rashba spin-orbit effect originating from the inversion asymmetry can give rise to the spin polarization. The spin polarization does not increase linearly but shows obvious resonant features as the strength of Rashba spin-orbit coupling increases, and the amplitudes of spin polarization can reach the highest around the first resonant energy level. Furthermore, it is found that electrons with different spin orientations will spend quite different time through the same heterostructures. The difference of the dwell time between spin-up and spin-down electrons arise from the Rashba spin-orbit coupling. And it is also found that the dwell time will reach its maximum at the first resonant energy level. It can be concluded that, in the time domain, the tunneling processes of the spin-up and spin-down electrons can be separated by modulating the strength of Rashba spin-orbit coupling. Study results indicate that Rashba spin-orbit effect can cause a nature spin filter mechanism in the time domain.     

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.     

The effect of k-cubic Dresselhaus spin–orbit coupling on the decay time of persistent spin helix states in semiconductor two-dimensional electron gases

We study the theoretical effect of k-cubic （i.e, cubic-in-momentum） Dresselhaus spin-orbit coupling on the decay time of persistent spin helix states in semiconductor two-dimensional electron gases. We show that the decay time of persistent spin helix states may be suppressed substantially by k-cubic Dresselhaus spin-orbit coupling, and after taking the effect of k-cubic Dresselhaus spin-orbit interaction into account, the theoretical results obtained accord both qualitatively and quantitatively with other recent experimental results.     

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

The effect of Dresselhauss spin-orbit coupling on transport and thermodynamic properties of a non-interacting two-dimensional electron gas (2DEG) is investigated. The Hamiltonian used also includes a tilted magnetic field and a Rashba spin-orbit interaction. The Dresselhauss spin-orbit interaction, likewise the Rashba spin-orbit interaction, introduces a beating pattern in the conductivity tensor and in the magnetization along the field direction. A method to estimate the contribution of the Rashba and Dresselhauss interactions to the beating pattern is given using the periodicity of the beating patterns.     

Spin Hall and spin Nernst effects in graphene with intrinsic and Rashba spin-orbit interactions

The spin Hall and spin Nernst effects in graphene are studied based on Green’s function formalism.We calculate intrinsic contributions to spin Hall and spin Nernst conductivities in the Kane-Mele model with various structures.When both intrinsic and Rashba spin-orbit interactions are present,their interplay leads to some characteristics of the dependence of spin Hall and spin Nernst conductivities on the Fermi level.When the Rashba spin-orbit interaction is smaller than intrinsic spin-orbit coupling,a weak kink in the conductance appears.The kink disappears and a divergence appears when the Rashba spin-orbit interaction enhances.When the Rashba spin-orbit interaction approaches and is stronger than intrinsic spin-orbit coupling,the divergence becomes more obvious.     

多层结构双自旋过滤隧道结中的电子输运特性

在转移矩阵方法及Mireles和Kirczenow的量子相干输运理论的基础上,研究了正常金属层/磁性半导体层/非磁绝缘层/磁性半导体层/正常金属层型双自旋过滤隧道结中Rashba自旋轨道耦合效应和自旋过滤效应对自旋相关输运的影响.讨论了隧穿磁电阻（TMR）、隧穿电导与各材料层厚度、Rashba自旋轨道耦合强度以及两磁性半导体中磁矩的相对夹角θ之间的关系.研究表明：含磁性半导体层的双自旋过滤隧道结由于磁性半导体层的自旋过滤效应和Rashba自旋轨道耦合作用可获得极大的TMR值.另外TMR和隧穿电导随着Rashba自旋轨道耦合强度的变化而振荡,振荡周期随Rashba自旋轨道耦合强度的增大逐渐减小. 关键词： 双自旋过滤隧道结 Rashba自旋轨道耦合 隧穿磁电阻 隧穿电导     

含δ势垒的铁磁/半导体/铁磁异质结中的自旋输运和渡越时间

研究了含δ势垒的铁磁/半导体/铁磁异质结中自旋相关的透射概率和渡越时间,讨论了量子尺寸效应和Rashba自旋轨道耦合效应对隧穿特性的影响.研究结果表明：δ势垒的存在降低了自旋电子的透射概率,改变了透射概率的位相.Rashba自旋轨道耦合强度的增加加大了透射概率的振荡频率.不同自旋取向的电子隧穿异质结时,渡越时间随着半导体长度、Rashba自旋轨道耦合强度以及两铁磁电极中的磁化方向的夹角的变化而变化. 关键词： δ势垒')" href="#">δ势垒 铁磁/半导体/铁磁异质结 Rashba自旋轨道耦合效应 渡越时间     

Intersubband spin-orbit coupling and spin splitting in symmetric quantum wells

In semiconductors with inversion asymmetry, spin-orbit coupling gives rise to the well-known Dresselhaus and Rashba effects. If one considers quantum wells with two or more conduction subbands, an additional, intersubband-induced spin-orbit term appears whose strength is comparable to the Rashba coupling, and which remains finite for symmetric structures. We show that the conduction band spin splitting due to this intersubband spin-orbit coupling term is negligible for typical III-V quantum wells.     

The effects of Dresselhaus and Rashba spin-orbit interactions on the electron tunneling in a non-magnetic heterostructure

We theoretically investigate the electron transport properties in a non-magnetic heterostructure with both Dresselhaus and Rashba spin-orbit interactions. The detailed-numerical results show that (1) the large spin polarization can be achieved due to Dresselhaus and Rashba spin-orbit couplings induced splitting of the resonant level, although the magnetic field is zero in such a structure, (2) the Rashba spin-orbit coupling plays a greater role on the spin polarization than the Dresselhaus spin-orbit interaction does, and (3) the transmission probability and the spin polarization both periodically change with the increase of the well width.     

Band structures of carbon nanotube with spin-orbit coupling interaction

We explore the band structures of single-walled carbon nanotubes (SWCNTs) with two types of spin-orbit couplings. The obtained results indicate that weak Rashba spin-orbit coupling interaction can lead to the breaking of four-fold degeneracy in all tubes even though without the intrinsic SO coupling. The asymmetric splitting between conduction bands and valence bands is caused by both SO couplings at the same time. When the ratio of Rashba spin-orbit coupling to the intrinsic spin-orbit coupling is larger than 3, metallic zigzag nanotube is always metallic conductor, on the contrary it becomes semiconducting properties. However, only when this ratio is equal to about 3 or the intrinsic spin-orbit coupling is much weak, the metallic armchair nanotube still holds the metallic behavior in transport.     

Nondissipative spin Hall effect via quantized edge transport

The spin Hall effect in a two-dimensional electron system on honeycomb lattice with both intrinsic and Rashba spin-orbit couplings is studied numerically. Integer quantized spin Hall conductance is obtained at the zero Rashba coupling limit when electron Fermi energy lies in the energy gap created by the intrinsic spin-orbit coupling, in agreement with recent theoretical prediction. While nonzero Rashba coupling destroys electron spin conservation, the spin Hall conductance is found to remain near the quantized value, being insensitive to disorder scattering, until the energy gap collapses with increasing the Rashba coupling. We further show that the charge transport through counterpropagating spin-polarized edge channels is well quantized, which is associated with a topological invariant of the system.     

Effects of the Rashba spin-orbit coupling on Hofstadter's butterfly

We study the effect of Rashba spin-orbit coupling on the Hofstadter spectrum of a two-dimensional tight-binding electron system in a perpendicular magnetic field. We obtain the generalized coupled Harper spin-dependent equations which include the Rashba spin-orbit interaction and solve for the energy spectrum and spin polarization. We investigate the effect of spin-orbit coupling on the fractal energy spectrum and the spin polarization for some characteristic states as a function of the magnetic flux α and the spin-orbit coupling parameter. We characterize the complexity of the fractal geometry of the spin-dependent Hofstadter butterfly with the correlation dimension and show that it grows quadratically with the amplitude of the spin-orbit coupling. We study some ground state properties and the spin polarization shows a fractal-like behavior as a function of α, which is demonstrated with the exponent close to unity of the decaying power spectrum of the spin polarization. Some degree of spin localization or distribution around +1 or -1, for small spin-orbit coupling, is found with the determination of the entropy function as a function of the spin-orbit coupling. The excited states show a more extended (uniform) distribution of spin states.     

Spin Accumulation in a Rashba Nanoribbon

We investigate theoretically the spin accumulation in a Rashba spin-orbit coupling （SOC） nanoribbon nonadiabatically connected to a normal conductor. Both the nanoribbon and conductor are described by a hard-wall confining potential. Using the scattering matrix approach within the effective free-electron approximation, we have calculated the out-of-plane spin accumulation in the nanoribbon. It is found that the spin accumulation shifts toward the two edges of nanoribbon with the increasing of propagation modes. Specifically, as the Rashba SOC strength increases the spin accumulation in the nanoribbon will be enhanced and this result may suggest us a simple method to control the spin accumulation of the system by Rashba SOC strength.     

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).     

Effect of Rashba spin-orbit coupling on the spin-polarized transport in ferromagnet/semiconductor double tunnel junctions

Considering the Rashba spin-orbit interaction in the semiconductor, we study theoretically the spin-polarized transport in a two-dimensional ferromagnetic semiconductor double tunnel junctions by a quantum-mechanical approach. It is found that the transmission coefficient shows typical resonant transmission properties and the Rashba spin-orbit coupling has great different influences on the transmission coefficients of electrons with spin-up and down and tunnelling magnetoresistance (TMR). More importantly, the TMR is significantly enhanced by increasing the spin-orbit coupling, which is very useful for the designing of magnetic digital and memory sensor.     

AlGaN/GaN量子阱中子带的Rashba自旋劈裂和子带间自旋轨道耦合作用研究

首先把本征值方程投影到导带的子空间中, 进而得到AlGaN/GaN量子阱中第一、二子带的Rashba自旋劈裂系数(α ₁, α ₂)和子带间自旋-轨道耦合系数η₁₂. 然后自恰求解薛定谔方程和泊松方程计算了不同栅压的量子阱中的α ₁, α ₂和η₁₂, 并分别讨论了量子阱阱层、左右异质结界面和垒层对它们的贡献. 结果表明可以通过栅压来调节自旋-轨道耦合系数, 子带间自旋轨道耦合系数η₁₂比Rashba自旋劈裂系数α ₁, α ₂小, 但基本在同一数量级.     

Quantum dot with spin-orbit interaction in noncommutative phase space and analog Landau levels

We have studied a quantum dot with Rashba spin-orbit interaction in noncommutative phase space. The energy eigenvalues are analogous to Landau energy levels. It is shown that this system is related with a physically realizable model of a quantum dot with Rashba spin-orbit interaction in a magnetic field whereby a relation is derived among the noncommutative parameters, spin-orbit coupling strength and magnetic field.