The conductance and polarization in quantum wires with Rashba and Dresselhaus spin-orbit interactions

The conductance and polarization are studied in one-dimensional ballistic quantum wire with both Rashba and Dresselhaus spin-orbit interactions.Two kinds of structures are considered in the present work,one with mixture of two interactions and the other with sequence structure of them.We find that the conductance and polarization are strongly affected by these two interactions.With both interactions we obtain a multi-peak contour of spin polarization and a dramatic oscillation pattern of spin conductance,which are due to the different combination of the two spin-orbit interactions.

Pure spin polarized transport based on Rashba spin orbit interaction through the Aharonov Bohm interferometer embodied four-quantum-dot ring

The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm （AB） interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device.

Thermopower in parallel double quantum dots with Rashba spin-orbit interaction

Based on the Green＇s function technique and the equation of motion approach, this paper theoretically studies the thermoelectric effect in parallel coupled double quantum dots （DQDs）, in which Rashba spin-orbit interaction is taken into account. Rashba spin^rbit interaction contributions, even in a magnetic field, are exhibited obviously in the double quantum dots system for the thermoelectric effect. The periodic oscillation of thermopower can be controlled by tunning the Rashba spin^rbit interaction induced phase. The interesting spin-dependent thermoelectric effects will arise which has important influence on thermoelectric properties of the studied system.

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.

Nonlocal Andreev reflection with Rashba spin-orbital interaction in a triple-quantum-dot ring

We theoretically studied the nonlocal Andreev reflection with Rashba spin-orbital interaction in a triple-quantumdot （QD） ring, which is introduced as Rashba spin-orbital interaction to act locally on one component quantum dot. It is found that the electronic current and spin current are sensitive to the systematic parameters. The interdot spin-flip term does not play a leading role in causing electronic and spin currents. Otherwise the spin precessing terra leads to shift of the peaks of the the spin-up and spin-down electronic currents in different directions and results in the spin current. Moreover, the spin-orbital interaction suppresses the nonlocal Andreev reflection, so we cannot obtain the pure spin current.

含Rashba-Dresselhaus双阶梯型量子线中电子的自旋电导开关效应

利用紧束缚近似的非平衡格林函数法,研究了含Rashba和Dresselhaus自旋轨道耦合效应的双阶梯型量子线中电子的自旋电导开关效应.结果表明在正向偏压下,系统有大的自旋电导出现;但在反向偏压下,这个大的自旋电导会消失.并且自旋电导随着Rashba和Dresselhaus自旋轨道耦合效应的变化呈现圆形结构,表明Rashba和Dresselhaus自旋轨道耦合效应引起自旋电导的作用是一样的,因此可以通过调节Rashba或Dresselhaus自旋轨道耦合效应来控制自旋电导.该系统在未来有可能用来制作全电自旋电导开关的量子线.

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 pwave 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.

Spin flip in single quantum ring with Rashba spin–orbit interation

We theoretically investigate spin transport in the elliptical ring and the circular ring with Rashba spin-orbit interaction. It is shown that when Rashba spin-orbit interaction is relatively weak, a single circular ring can not realize spin flip, however an elliptical ring may work as a spin-inverter at this time, and the influence of the defect of the geometry is not obvious. Howerver if a giant Rashba spin-orbit interaction strength has been obtained, a circular ring can work as a spin-inverter with a high stability.

Topological phase in one-dimensional Rashba wire

We study the possible topological phase in a one-dimensional（1D） quantum wire with an oscillating Rashba spin–orbital coupling in real space. It is shown that there are a pair of particle–hole symmetric gaps forming in the bulk energy band and fractional boundary states residing in the gap when the system has an inversion symmetry. These states are topologically nontrivial and can be characterized by a quantized Berry phase ±π or nonzero Chern number through dimensional extension. When the Rashba spin–orbital coupling varies slowly with time, the system can pump out 2 charges in a pumping cycle because of the spin flip effect. This quantized pumping is protected by topology and is robust against moderate disorders as long as the disorder strength does not exceed the opened energy gap.

Rashba效应影响下InAs/GaAs自组织量子点中极化子性质

考虑Rashab自旋—轨道相互作用对半导体量子点中极化子基态能量的影响.采用LLP中耦合的方法处理了电子—声子相互作用.结果表明由于Rashba效应的影响使得极化子的基态能量分列为上下两支而且Rashba自旋—轨道相互作用能与总的基态能及其它能量成分间的比例关系,随电子波矢K变化非常显著.Rashba自旋—轨道相互用作使得量子点中极化子基态能量在无任何外磁场的情况下发生分裂,所以完全不同于强磁场影响下的简单Zeeman效应,然而,自旋—轨道相互作用引起的分裂有时掺杂着Zeeman分裂,因此它引起的分裂属于复杂分裂.声子对总能量的贡献为负,由于声子的存在极化子争裂能较裸电子更为稳定.

Rashba效应影响下量子点中弱耦合束缚极化子的性质

采用改进的线性组合算符和幺正变换的方法研究了Rashba效应影响下量子点中弱耦合束缚极化子的性质,导出了Rashba效应影响下量子点中弱耦合束缚极化子的振动频率、有效质量、基态分裂能和相互作用能.数值计算结果表明随Rashba自旋-轨道耦合常数的增加,由于声子作用产生的附加能量对零磁场时自旋分裂能的影响占有绝对优势.库仑势对束缚极化子的基态能量的影响同时也占有绝对优势.所以,研究Rashba自旋轨道相互作用时声子的影响不可忽略.

Rashba效应影响下半导体量子点中强耦合极化子的声子平均数

采用改进的线性组合算符方法,研究了Rashba效应影响下半导体量子点中强耦合极化子的光学声子平均数.导出在电子-体纵光学声子(LO)强耦合时抛物量子点中极化子的光学声子平均数、振动频率、相互作用能和有效质量随受限强度和Rashba自旋-轨道耦合常数的变化.数值计算结果表明Rashba自旋-轨道相互作用使极化子的有效质量、基态能分裂为上下两支,随耦合常数的增加极化子基态能量、有效质量表现为增加和较少两种截然相反的情形;Rashba自旋-轨道相互作用影响下强耦合极化子的光学声子平均数随量子点的受限强度、电子声子耦合强度增大而增大,极化子的相互作用能随受限强度的增加先急剧增加,当达到极值后随受限强度的增加而急剧减少.

Rashba效应影响下半导体量子点中弱耦合极化子的性质

采用改进的线性组合算符和幺正变换的方法研究Rashba效应影响下量子点中弱耦合极化子的性质.导出了Rashba效应影响下量子点中弱耦合极化子的振动频率、有效质量、基态分裂能和相互作用能.数值计算结果表明表明随Rashba自旋-轨道耦合常数α_R的增加由于声子作用产生的附加能量能对零磁场下自旋分裂能的影响占有绝对优势.所以,研究Rashba自旋轨道相互作时声子的影响不可忽略.

考虑Rashba效应自组织量子点中极化子性质

在对半导体量子点的研究中考虑自旋-轨道相互作用对极化子基态能量的影响.采用LLP变分的方法研究了电子-声子相互作用.结果表明声子对极化子基态能量起了很重要的作用,而且由于极化子分裂能对极化子基态能量的贡献很大,故在量子点中研究极化子性质时不可忽略极化子分裂能的影响.自旋分裂能随动量增加呈抛物线型增加.随Rashba自旋轨道耦合常数的增加极化子基态能量表现为增加和减少两种截然相反的情况,而两个分裂态中自旋向下的能态更稳定.Rashba效应不可忽略.

量子点环Aharonov-Bohm干涉器中的电子自旋极化输运

采用非平衡态格林函数方法,研究了四量子点环嵌入AB干涉器中,由局域Rashba自旋轨道耦合诱导的电子自旋极化输运。在体系处于平衡态的情况下,当电子从"源"电极经量子点区到"漏"电极时,通过调节穿过AB干涉器的磁通和量子点上的局域Rashba自旋轨道耦合强度,输运电子的两种自旋态出现了完全极化现象。同时,量子点内的库仑相互作用对体系的自旋输运性质有重要影响。

有Rashba自旋—轨道相互作用的一维介观环哈密顿量的离散化

有Rashba自旋—轨道相互作用的一维环上,将运动电子的哈密顿量离散化。在正常区域,用没有争议的定义来计算持续的自旋流,将计算持续自旋流的公式也进行离散化。用离散化的近似方法也可以计算介观环中的持续自旋流。

Rashba多量子阱异质结中自旋轨道耦合效应对电子输运的影响

根据量子相干输运理论,利用传递矩阵的方法,研究自旋电子在铁磁体(F)/半导体多量子阱(SWM)/铁磁体的一维结构中,考虑自旋轨道耦合效应时的量子相干输运的特性.通过计算发现在这种一维多量子阱结构中的自旋电子的输运特性发生了一定的变化,这有利于进一步提高自旋电子的隧穿系数和自旋极化率.

Thermodynamic behaviour of Rashba quantum dot in the presence of magnetic field

The thermodynamic properties of an In Sb quantum dot have been investigated in the presence of Rashba spin–orbit interaction and a static magnetic field. The energy spectrum and wave-functions for the system are obtained by solving the Schrodinger wave-equation analytically. These energy levels are employed to calculate the specific heat, entropy,magnetization and susceptibility of the quantum dot system using canonical formalism. It is observed that the system is susceptible to maximum heat absorption at a particular value of magnetic field which depends on the Rashba coupling parameter as well as the temperature. The variation of specific heat shows a Schottky-like anomaly in the low temperature limit and rapidly converges to the value of 2kB with the further increase in temperature. The entropy of the quantum dot is found to be inversely proportional to the magnetic field but has a direct variation with temperature. The substantial effect of Rashba spin–orbit interaction on the magnetic properties of quantum dot is observed at low values of magnetic field and temperature.

Rashba自旋-轨道相互作用影响下量子盘中强耦合磁极化子性质的研究

本文基于Lee-Low-Pines幺正变换法,采用Tokuda改进的线性组合算符法研究了Rashba自旋-轨道相互作用效应下量子盘中强耦合磁极化子的性质.结果表明,磁极化子的相互作用能Eint的取值随量子盘横向受限强度ω0、外磁场的回旋频率ωc、电子-LO声子耦合强度α和量子盘厚度L的变化均与磁极化子的状态性质密切相关;磁极化子的平均声子数N随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在Rashba自旋-轨道相互作用效应影响下磁极化子的有效质量将劈裂为m*+,m*-两种,它们随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在研究量子盘中磁极化子问题时,电子-LO声子耦合和Rashba自旋-轨道相互作用效应的影响不可忽略,但Rashba自旋-轨道相互作用和极化子效应对磁极化子的影响只有在电子运动的速率较慢时显著.

纳米环中基于自旋轨道耦合的自旋过滤效应

理论研究纳米尺度半导体量子环中的电子自旋极化输运现象。量子环的每个臂上生长一个半导体量子点,其中存在Rashba自旋轨道耦合相互作用。在外加磁通的联合作用下,流过体系的自旋朝上和朝下的电子将获得不同的相位,从而发生不同的干涉效应。在适当调控体系参数的情况下,只能有一种自旋取向的电子通过,即发生了自旋过滤效应。此结构能在现有的实验条件下实现,并有望能得到实际的应用。