Spin-Tunneling Time in Ferromagnetic/Semiconductor/Ferromagnetic Three-Terminal Heterojunction in the Presence of Rashba Spin-Orbit Coupling

We study theoretically the transmission coefficients and the spin-tunneling time in ferromagnetic/semiconductor/ferromagnetic three-terminal heterojunction in the presence of Rashba spin-orbit interaction, in which onedimensional quantum waveguide theory is developed and applied. Based on the group velocity concept and the particle current conservation principle, we calculate the spin-tunneling time as the function of the intensity of Rashba spin-orbit coupling and the length of the semiconductor. We find that as the length of the semiconductor increases, the spintunneling time does not increase linearly but shows behavior of slight oscillation. Furthermore, with the increasing of the spin-orbit coupling, the spin-tunneling time increases.     

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     

铁磁/半导体(绝缘体)/铁磁异质结中渡越时间与两铁磁层磁矩夹角变化的关系

在群速度概念的基础上, 研究了自旋极化电子隧穿通过铁磁体/半导体(绝缘体)/铁磁体异质结时, 渡越时间随两端铁磁层中磁矩夹角变化的关系. 研究结果表明: 当中间层为半导体层时, 由于半导体层中的Rashba自旋轨道耦合强度的影响, 自旋向上电子和自旋向下电子的渡越时间差会在两铁磁层相对磁矩夹角为π/2和3π/2附近出现一个极小值. 当中间层为绝缘体层时, 势垒高度的变化会导致不同取向的自旋极化电子渡越时间差的变化, 并当势垒高度超过一临界值时发生翻转. 关键词： 铁磁体/半导体(绝缘体)/铁磁体异质结 Rashba自旋轨道耦合强度 渡越时间 磁矩     

Spin transfer torque in the semiconductor/ferromagnetic structure in the presence of Rashba effect

Spin transfer torque in magnetic structure occurs when the transverse component of the spin current that flows from the nonmagnetic medium to ferromagnetic medium is absorbed by the interface. In this paper, considering the Rashba effect on the semiconductor region, we discuss the spin transfer torque in semiconductor/ferromagnetic structure and obtain the components of spin-current density for two models:(i) single electron and(ii) the distribution of electrons. We show that no matter whether the difference in Fermi surface between semiconductor and Fermi spheres for the up and down spins in ferromagnetic increases, the transmission probability decreases. The obtained results for the values used in this article illustrate that Rashba effect increases the difference in Fermi sphere between semiconductor and Fermi sphere for the up and down spins in ferromagnetic. The results also show that the Rashba effect, brings an additional contribution to the components of spin transfer torque, which does not exist in the absence of the Rashba interaction. Moreover, the Rashba term has also different effects on the transverse components of the spin torque transfer.     

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.     

The spin-double refraction in two-dimensional electron gas

We briefly review the phenomenon of the spin-double refraction that originates at an interface separating a two-dimensional electron gas with Rashba spin–orbit coupling from a one without. We demonstrate how this phenomenon in semiconductor heterostructures can produce and control a spin-polarized current without ferromagnetic leads.     

Tunnel barrier and noncollinear magnetization effects on shot noise in ferromagnetic/semiconductor/ferromagnetic heterojunctions

Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers.     

铁磁/半导体/铁磁结构的双量子环自旋输运的特性

研究了与铁磁/半导体/铁磁结构相关的双量子环自旋输运的规律,研究结果表明：总磁通为零条件下,铁磁电极磁化方向反平行时,双量子环与单量子环相比提高了自旋电子透射概率的平均值.铁磁电极磁化方向平行时,双量子环对提高自旋向下电子平均透射概率的效果更明显;双量子环受到Rashba自旋轨道耦合作用影响时,自旋电子的平均透射概率明显高于单量子环,即使再加上外加磁场的影响,透射概率较高这一特征依然存在;双量子环所含的δ势垒具有阻碍自旋电子输运的作用,随δ势垒强度Z的增大透射概率 关键词： 双量子环 Rashba自旋轨道耦合 透射概率 δ势垒')" href="#">δ势垒     

自旋轨道耦合和磁场对准一维铁磁/半导体/铁磁系统中电子输运性质的影响

利用传递矩阵方法，我们计算了自旋轨道耦合和磁场对准一维铁磁/半导体/铁磁系统中电子输运性质的影响。计算结果发现，透射系数的振幅随磁场增加而增大。在反铁磁排列时，即使在磁场作用下，上、下自旋电子具有相同的透射系数。与不加磁场时的情况相反，在一定的磁场和耦合强度时，铁磁排列中，上自旋电子的透射系数大于下自旋电子的，而且出现了自旋反转。     

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.     

铁磁/反铁磁/铁磁三层膜系统中反铁磁自旋结构及其交换各向异性

研究铁磁/反铁磁/铁磁三层膜中界面存在二次以及双二次交换耦合下反铁磁磁矩转动及其交换各向异性.结果表明,其反铁磁膜中的磁矩转动存在可逆"恢复行为"、不可逆"连续倒转行为"以及不可逆"中断倒转行为"三种情形,三种情形的出现强烈地依赖于两界面处的线性耦合和双二次耦合.钉扎界面的交换耦合与旋转界面的交换耦合相互竞争,当钉扎界面耦合占主导时,反铁磁磁矩发生可逆"恢复行为",系统出现交换偏置.在旋转界面耦合占主导情形下,其线性耦合与双二次耦合也相互竞争,分别导致反铁磁磁矩发生不可逆"连续倒转行为"和不可逆"中断倒转行为",系统都不出现交换偏置,但矫顽场都得以增强.相关结论为实验上观测的磁滞能耗以及界面垂直耦合提供了可能的解释.     

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.     

Spin-dependent conductance in FM/quantum-dot/FM tunneling system

We present a theoretical study of the spin-dependent conductance spectra in a FM/semiconductor quantum-dot (QD)/FM system. Both the Rashba spin-orbit (SO) coupling in the QD and spin-flip scattering caused by magnetic barrier impurities are taken into account. It is found that in the single-level QD system with parallel magnetic moments in the two FM leads, due to the interference between different tunneling paths through the spin-degenerate level, a dip or a narrow resonant peak can appear in the conductance spectra, which depends on the property of the spin-flip scattering. When the magnetizations of the two FM leads are noncollinear, the resonant peak can be transformed into a dip. The Rashba SO coupling manifests itself by a Rashba phase factor, which changes the phase information of every tunneling path and can greatly modulate the conductance. When the QD has multiple levels, the Rashba interlevel spin-flip effect appears, which changes the topological property of the structure. Its interplay with the Rashba phase can directly tune the coupling strengths between dot and leads, and can result in switching from resonance into antiresonance in the conductance spectra.     

Conductance Oscillations in Spin Field-Effect Transistors

Ballistic spin transport in spin field-effect transistors is studied by taking into account the Rashba spinorbit coupling, interracial scattering, and band mismatch. It is shown that the spin conductance oscillation with the semiconductor channel length is a superimposition of the Rashba spin precession and spin interference oscillations. They have different oscillation periods π/κR and π/κ with κR the Rashba wavevector and κ the Fermi wavevector of the semiconductor channel, and play different parts of slow and rapid oscillations, depending upon the relative magnitude of π/κR and π/κ. Only at κ = κR does the spin conductance exhibit oscillations of a single period. Two types of different behaviors of the tunnelling magnetoresistance are discussed.     

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     

Effect of Rashba spin–orbit coupling on the spin polarized transport in diluted magnetic semiconductor barrier structures

We investigate theoretically the effects of Rashba spin–orbit coupling on the spin dependent transport through diluted magnetic semiconductor single and double barrier structures in the presence of a magnetic field. We find that the Rashba spin–orbit coupling gives rise to an enhancement of the negative tunnelling magnetoresistance of the diluted magnetic semiconductor single barrier structure and a pronounced beating pattern in the tunnelling magnetoresistance and spin polarization of the diluted magnetic semiconductor double barrier structure.     

外应力场下双层铁磁薄膜中的铁磁共振性质

用铁磁共振方法得到了双层铁磁薄膜的色散关系解析表达式.发现共振场依赖于层间耦合强度和应力场.假定层间为反铁磁性耦合，且铁磁层Ａ有较强的平面内各向异性.随着外磁场的增强，铁磁层Ｂ中的磁化强度突然由最初的反平行转为平行，从而导致色散曲线的阶跃，并且发现光学模阶跃幅度比声学模大.随着应力场的增强，Ｂ层中磁化强度反转所需的外磁场减弱.此外，在不同的交换耦合强度和应力场下，光学模共振场对外磁场方向的依赖性较强. 关键词： 双层铁磁薄膜 界面相互作用 应力各向异性场 铁磁共振     

Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N量子阱中的Rashba自旋劈裂

正如人们所知, 可以通过电场或者设计非对称的半导体异质结构来调控体系的结构反演不对称性(SIA)和Rashba自旋劈裂. 本文研究了Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中第一子带的Rashba 系数和Rashba自旋劈裂随Al_0.3Ga_0.7N插入层(右阱)的厚度w_s以及外加电场的变化关系, 其中GaN层(左阱)的厚度为40-w_s Å. 发现随着w_s的增加, 第一子带的Rashba系数和Rashba自旋劈裂首先增加, 然后在w_s>20 Å 时它们迅速减小, 但是w_s>30 Å时Rashba自旋劈裂减小得更快, 因为此时k_f也迅速减小. 阱层对Rashba系数的贡献最大, 界面的贡献次之且随w_s变化不是太明显, 垒层的贡献相对比较小. 然后, 我们假w_s=20 Å, 发现外加电场可以很大程度上调制该体系的Rashba系数和Rashba自旋劈裂, 当外加电场的方向同极化电场方向相同(相反)时, 它们随着外加电场的增加而增加(减小). 当外加电场从-1.5×10⁸ V·m^-1到1.5×10⁸ V· m^-1变化时, Rashba系数随着外加电场的改变而近似线性变化, Rashba自旋劈裂先增加得很快, 然后近似线性增加, 最后缓慢增加. 研究结果表明可以通过改变GaN层和Al_0.3Ga_0.7N层的相对厚度以及外加电场来调节Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中的Rashba 系数和Rashba自旋劈裂, 这对于设计自旋电子学器件有些启示.     

Magnetic Properties and Antiferromagnetic Coupling in Inhomogeneous Zn1-xFexO Magnetic Semiconductor

Zn1-xFexO inhomogeneous oxide magnetic semiconductor films with high Fe concentration are prepared by sputtering, and fast annealing is carried out at different temperatures. It is found that magnetic properties are greatly modulated by controlling the composition inhomogeneity and subsequently fast annealing. Both ferromagnetic and paramagnetie components are found to coexist in the as-deposited Zn1-xFexO magnetic semiconductor. In particular, the antiferromagnetic coupling between the neighbouring local ferromagnetic regions is found in the as-deposited Zn0.23Fe0.77O film, and the antiferromagnetic coupling strength increases with increasing temperature from 110K to 300 K. We believe that this unusual antiferromagnetic coupling is mediated by thermally activated hopping carriers.     

Quantum transport in ferromagnetic graphene super lattice in the presence of Rashba spin–orbit coupling

Using the transfer matrix method, we study the electron transport through a single-layer graphene superlattice with alternating layers of ferromagnetic and normal regions with Rashba spin–orbit coupling. We show that the transport properties of the system depend strongly on the superlattice parameters. As another result, Rashba spin–orbit coupling manifests to be of crucial importance in controlling the transmission probabilities and Giant Magneto Resistance (GMR).