自旋电子学简介及其研究进展

自旋电子学主要研究电子自旋在固体物理中的作用,是一门结合磁学与微电子学的交叉学科,其研究对象包括电子的自旋极化、自旋相关散射、自旋弛豫以及与此相关的性质及其应用等.基于电子自旋的自旋电子器件能够大大提高信息处理速度和存储密度,而且具有非易失性、低能耗等优点.简单介绍了自旋电子学的概念及其研究内容,综述了自旋电子学目前的研究及应用进展.     

磁电垒结构中自旋极化输运性质的研究

研究了电子隧穿几类磁电垒结构的自旋极化输运性质，导出统一的传输概率公式，揭示了非 均匀磁场的分布与自旋过滤的关系，同时表明采用有效朗德因子较大的半导体材料可以显著 增强磁电垒结构的自旋过滤效果. 关键词： 磁电垒 自旋过滤 自旋电子学 自旋极化     

稀磁半导体--自旋和电荷的桥梁

稀磁半导体可能同时利用载流子的自旋和电荷自由度构造将磁、电集于一体的半导体器件．尤其是铁磁半导体材料的出现带动了半导体自旋电子学的发展．室温铁磁半导体材料的制备，半导体材料中有效的自旋注入，以及自旋在半导体结构中输运和操作已成为目前半导体自旋电子学领域中的热门课题．稀磁半导体呈现出强烈的自旋相关的光学性质和输运性质，这些效应为人们制备半导体自旋电子学器件提供了物理基础．     

电子是圆的吗？

 许多人想象认为,电子是圆形球对称的自旋的点粒子。然而,假如电子具有偶极矩,这将打破通常的图像,圆形将被拉长而变成椭圆形。现在,英国伦敦帝国大学的J.J.哈德孙(J. J. Hudson)与他的同事一起,利用超冷的氟化钇分子设置了电子的电偶极矩(edm)的最低值。分子的edm 值反映了非成对的电子的可能的偶极矩。     

量子阱中电子自旋注入及弛豫的飞秒光谱研究

采用飞秒脉冲的饱和吸收光谱方法研究了GaAs/AlGaAs多量子阱中电子自旋的注入和 弛豫特性，测得电子自旋极化弛豫时间为80±10ps.说明了电子自旋 轨道耦合相互作用引 起局域磁场的随机化，是导致电子的自旋极化弛豫的主要机理. 关键词： 自旋电子学 半导体量子阱 飞秒激光光谱 自旋 轨道耦合     

自旋电子学和计算机硬件产业

1988年发现巨磁电阻（GMR）效应，是基于自旋的新电子学的开始。文章介绍观察效应的物理基础，以及这些效应和材料在信息存储上的应用。GMR硬盘（HDD）已经形成了数十亿美元的工业；其后发现的室温隧道磁电阻（TMR）效应已用于制造新关磁随机存储器（MRAM），它正在开创另一个数十亿美元的工业。自旋电子学研究的物理对象是自旋向上和自旋向下的载流子，而传统半导体电子学的对象是电荷为正和电荷为负的载流子，即空穴和电子。电子自旋特性进入半导体电子学，为新的器件创造了机会。为了成功地将电子自旋结合到半导体微电子技术中去，需要解决磁性原子自旋极化状态的控制，以及自旋极化载流子电流的有效注入、传输、控制、操纵和检测。评述了基于电子自旋的新器件原理、新材料的探索以及自旋相干态的光学操纵。     

自旋电子学和自旋流

传统的电子学完全忽略了电子自旋,这使人们在探索未来半导体工业发展时有了新的契机和可能的研究方向.自旋电子学旨在利用电子自旋而非传统的电子电荷为基础, 探讨研发新一代电子产品的可能性.文章简单介绍了自旋电子学的动机、物理基础以及研究内容,并重点介绍了在自旋电子学器件中起关键作用的自旋流.文章从自旋流的定义、它能产生的物理性质和最近有关自旋流探测的理论和实验进展等三个方面进行阐述.     

磁性纳米电机单电子晶体管的自旋输运特性

文章作者在研究磁性隧道结的自旋输运中引入量子点的机械振动自由度,将单电子隧穿和振动自由度耦合所导致的shuttle输运理论应用到自旋电子学中,研究结果表明,shuttle输运对自旋极化输运有很大的影响,其独特的输运性质可以用来设计自旋电子器件,文章在理论上提出具有巨磁效应的自旋阀、高性能的半导体自旋注入器以及电流的整流器.     

自旋电子学研究与进展

自旋电子学是最近几年在凝聚态物理中发展起来的新学科分支，它研究在固体中自旋自由度的有效控制和操纵，在金属和半导体中自旋极化、自旋动力学、自旋极化的输运和自旋电子检测．由于它在信息存储方面的重大应用前景，受到学术界和工业界的高度重视．文章扼要地介绍了自旋电子学发展的历程和发展中的最重要的发现．最近几年，最奇特的发现和最重要的应用莫过于巨磁电阻，薄膜领域纳米技术的迅速发展使巨磁电阻的应用变成可能．作为磁记录头它已使硬磁盘的记录密度提高到170Gbit／in^2．动态随机存储器MRAM的研究已实现16Mbit的存储密度．     

有机自旋电子学

文章介绍了有机半导体同自旋电子学相结合的新学科——有机自旋电子学．着重讨论以下三个方面问题：有机半导体特别是有机共轭聚合物特性及其载流子性质；自旋电子学研究热点；有机自旋电子学研究进展．     

Consistency in formulation of spin current and torque associated with a variance of angular momentum

Based on the Noether's theorem, we develop systematically and rigorously the spin-dependent formulation of the conservation laws. The effect of the electronic polarization due to the spin-orbit coupling is included in the Maxwell equations. The polarization is related to the antisymmetric components of spin current, and it provides a possibility to measure the spin current directly. The variances of spin and orbit angular momentum currents imply a torque on the "electric dipole" associated with the moving electron. The dependencies of the torque on the polarization and the force on the motions of spin-polarized electrons in a two-dimensional electron gas with the Rashba spin-orbit coupling are discussed.     

Atomic Electric Dipole Moment Measurement Using Spin Exchange Pumped Masers of 129Xe and 3He

We have measured the T-odd permanent electric dipole moment of 129Xe with spin exchange pumped masers and a 3He comagnetometer. The comagnetometer provides a direct measure of several systematic effects that may limit electric dipole moment sensitivity, and we have directly measured the effects of changes in leakage current that result when the applied electric field is changed. Our result, d(129Xe) = 0.7+/-3.3(stat)+/-0.1(syst)x10(-27)e cm, is a fourfold improvement in sensitivity.     

Optical nuclear spin polarization in quantum dots

Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot(QD) by the coherent population trapping(CPT) and the electric dipole spin resonance(EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip–flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time.     

Spin cloud induced around an elastic scatterer by the intrinsic spin hall effect

Similar to the Landauer electric dipole created around an impurity by the electric current, a spin polarized cloud of electrons can be induced by the intrinsic spin Hall effect near a spin independent elastic scatterer. It is shown that in the ballistic range around the impurity, such a cloud appears in the case of Rashba spin-orbit interaction, even though the bulk spin Hall current is absent.     

Theoretical description of the spectroscopic properties of rare earth ions in crystals

In this article the present state of knowledge of the theory of one- and two-photon processes observed in rare earth ions in crystals is presented. The conclusions are based on the results of ab initio calculations performed for various ions across the lanthanide series. The model applied for the calculations is based on the Rayleigh–Schrödinger perturbation theory, and the amplitude of a certain electric dipole transition is expressed in terms of effective operators. The radial integrals of the effective operators are defined by the perturbed functions that contain the perturbing influence of single excitations from the 4f shell to all one-electron states of a given symmetry, discrete and continuum. In this approach the interactions between the 4f^N and the excited configurations via the crystal field potential, the electron correlation operator and the spin–orbit interaction operator are discussed; it is believed that the presented theory contains the most important physical mechanisms responsible for the f↔f electric dipole transitions. Two alternative formulations of the theory of one-photon electric dipole transitions are presented. Consequently, the transition amplitude is defined within the standard theory based on the length formula and within a new approach which is based on the velocity form of the electric dipole radiation operator.     

Motion of neutral fermions with anomalous magnetic and electric moments in external fields

A covariant spin operator is found for fermions with anomalous magnetic and electric dipole moments in constant external fields. The spin behavior of a neutral fermion in constant magnetic and electric fields is investigated using exact solutions obtained for the Dirac equation.     

g-factor tuning and manipulation of spins by an electric current

We investigate the Zeeman splitting of the two-dimensional electron gas in an asymmetric silicon quantum well, performing electron-spin-resonance (ESR) experiments. Applying a small dc current we observe a shift in the resonance field due to the additional current-induced Bychkov-Rashba type of spin-orbit field. We also show that a high frequency current may induce electric dipole spin resonance very efficiently. We identify different contributions to this type of ESR signal.     

Disturbance of spin equilibrium by current through the interface of noncollinear ferromagnets

Boundary conditions are derived that determine the penetration of spin current through an interface of two noncollinear ferromagnets with an arbitrary angle between their magnetization vectors. We start from the well-known transformation properties of an electron spin wave functions under the rotation of a quantization axis. It allows directly find the connection between partial electric current densities for different spin subbands of the ferromagnets. No spin scattering is assumed in the near interface region, so that spin conservation takes place when electron intersects the boundary. The continuity conditions are found for partial chemical potential differences in the situation. Spatial distribution of nonequilibrium electron magnetizations is calculated under the spin current flowing through a contact of two semi-infinite ferromagnets. The distribution describes the spin accumulation effect by current and corresponding shift of the potential drop at the interface. These effects appear strongly dependent on the relation between spin contact resistances at the interface.     

Zitterbewegung in Quantum Mechanics

The possibility that zitterbewegung opens a window to particle substructure in quantum mechanics is explored by constructing a particle model with structural features inherent in the Dirac equation. This paper develops a self-contained dynamical model of the electron as a lightlike particle with helical zitterbewegung and electromagnetic interactions. The model admits periodic solutions with quantized energy, and the correct magnetic moment is generated by charge circulation. It attributes to the electron an electric dipole moment rotating with ultrahigh frequency, and the possibility of observing this directly as a resonance in electron channeling is analyzed in detail. Correspondence with the Dirac equation is discussed. A modification of the Dirac equation is suggested to incorporate the rotating dipole moment.     

The magnetoelectric effect due to local noncentrosymmetry

Magnetoelectrics often possess ions located in noncentrosymmetric surroundings. Based on this fact we suggest a microscopic model of magnetoelectric interaction and show that the spin-orbit coupling leads to spin-dependent electric dipole moments of the electron orbitals of these ions, which results in non-vanishing polarization for certain spin configurations. The approach accounts for the macroscopic symmetry of the unit cell and is valid for both commensurate and complex incommensurate magnetic structures. The model is illustrated by the examples of MnWO(4), MnPS(3) and LiNiPO(4). Application to other magnetoelectrics is discussed.