A Scheme for Spin Manipulation in a Quantum Dot with Both Charge and Spin Bias

We propose a scheme for the effective polarization and manipulation of electron spin by using a quantum dot with both charge and spin bias. Using the equation of motion for Keldysh nonequilibrium Green function, we study the spin accumulation and polarization for the system. Through analytical analysis and a few numerical examples, it is demonstrated that fairly large spin accumulation and polarization can be produced due to the breakingsymmetry of the chemical potential for different electron spin in the leads. Moreover, the direction and the strength of the spin polarization can be conveniently controlled and tuned by varying the charge bias or the gate voltage.     

Spin density polarization effects in the presence of Coriolis force on ion acoustic waves in quantum plasma

Ion acoustic solitary waves in a quantum plasma, which is slowly rotating around an axis at an angle θ with the direction of magnetic field, are investigated. Quantum hydrodynamic model is under consideration with the effects of rotations which are included via Coriolis force. Fermions are degenerate and have different spin density states, that is, up and down characterized via parameter α. Linear analysis is performed by applying Fourier transformation to derive dispersion relation. For nonlinear analysis, we apply reductive perturbation method to derive Korteweg de Vries equation (KdV). The effects of variations of Coriolis force, spin polarization, and quantum parameter on characteristics of solitary structure are discussed. These results are applicable to astrophysical and laboratory plasmas.     

Quantum Correlations and Speed Limit of Central Spin Systems

In this article, single, and two-qubit central spin systems interacting with spin baths are considered and their dynamical properties are discussed. The cases of interacting and non-interacting spin baths are considered and the quantum speed limit (QSL) time of evolution is investigated. The impact of the size of the spin bath on the quantum speed limit for a single qubit central spin model is analyzed. The quantum correlations for (non-)interacting two central spin qubits are estimated and their dynamical behavior with that of QSL time under various conditions are compared. How QSL time could be availed to analyze the dynamics of quantum correlations is shown.     

A Suggestion for an Integrability Notion for Two-Dimensional Spin Systems

We suggest that trialgebraic symmetries might be a sensible starting point for a notion of integrability for two dimensional spin systems. For a simple trialgebraic symmetry we give an explicit condition in terms of matrices which a Hamiltonian realizing such a symmetry has to satisfy and give an example of such a Hamiltonian which realizes a trialgebra recently given by the authors in another paper. Besides this, we also show that the same trialgebra can be realized on a kind of Fock space of q-oscillators, i.e. the suggested integrability concept gets via this symmetry a close connection to a kind of noncommutative quantum field theory, paralleling the relation between the integrability of spin chains and two dimensional conformal field theory.     

Quantum Communication in Spin Chain with Multiple Spin Exchange Interaction

The transmission of quantum states in the anisotropic Heisenberg XXZ chain model with three-spin exchange interaction is studied. The average fidelity is used to evaluate the state transfer. It is found that quantum communication can be enhanced by the anisotropic coupling and multiple spin interaction. Such spin model can reduce the time required for the perfect state transmission where the fidelity is unity. The maximally entangled Bell states can be generated and separated from the whole quantum systems.     

纳米管中的自旋极化

结构缺陷、掺杂等可以导致纳米管的自旋极化,而自旋极化的纳米管可以利用载流子的自旋状态作为信息载体,实现一维的自旋电子传输.具有不同自旋极化结构的纳米管,根据其电子结构、自旋极化性质和输运性质的不同,可以用于实现不同用途的自旋电子器件.很多有关自旋极化的纳米管的理论和实验工作已经展开,然而其中仍有很多物理问题有待深入研究.     

纳米管中的自旋极化

结构缺陷、掺杂等可以导致纳米管的自旋极化，而自旋极化的纳米管可以利用载流子的自旋状态作为信息载体，实现一维的自旋电子传输。具有不同自旋极化结构的纳米管，根据其电子结构、自旋极化性质和输运性质的不同，可以用于实现不同用途的自旋电子器件。很多有关自旋极化的纳米管的理论和实验工作已经展开，然而其中仍有很多物理问题有待深入研究。     

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.     

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.     

Entanglement Negativity and Concurrence in Some Low-Dimensional Spin Systems

The influence of magnon bands on entanglement in the antiferromagnetic XXZ model on a triangular lattice, which models the bilayer structure consisting of an antiferromagnetic insulator and normal metal, is investigated. This effect was studied in ferromagnetic as well as antiferromagnetic triangular lattices. Quantum entanglement measures given by the entanglement negativity have been studied, where a magnon current is induced in the antiferromagnet due to interfacial exchange coupling between localized spins in the antiferromagnet and itinerant electrons in a normal metal. Moreover, quantum correlations in other frustrated models, namely the metal-insulation antiferromagnetic bilayer model and the Heisenberg model with biquadratic and bicubic interactions, are analyzed.     

Heisenberg-Integrable Spin Systems

We investigate certain classes of integrable classical or quantum spin systems. The first class is characterized by the recursively defined property P saying that the spin system consists of a single spin or can be decomposed into two uniformly coupled or disjoint subsystems with property P. For these systems the time evolution can be explicitly calculated. The second class consists of spin systems where all non-zero coupling constants have the same strength (spin graphs) possessing N − 1 independent, commuting constants of motion of Heisenberg type. These systems are shown to have the above property P and can be characterized as spin graphs not containing chains of length four as vertex-induced sub-graphs. We completely enumerate and characterize all spin graphs up to N = 5 spins. Applications to the construction of symplectic numerical integrators for non-integrable spin systems are briefly discussed.      

一维铁磁/有机共轭聚合物的自旋极化研究

针对最近关于自旋注入有机体的实验研究，理论上计算了有机分子与磁性原子接触时的自旋极化现象.通过调节磁性原子的自旋劈裂强度，发现有机分子链内的自旋极化弱于金属链，但强于半导体链.同时还研究了有机分子链内自旋极化随电子-声子耦合强度的变化关系以及界面耦合的自旋相关效应. 关键词： 界面耦合 自旋极化 自旋劈裂     

Spin squeezing and quantum correlations

We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.     

磁台阶势垒结构中二维电子气的自旋极化输运

运用散射矩阵方法,研究了台阶磁势垒量子结构中二维电子气的隧穿输运性质.结果表明：在零偏压下,电子传输概率的自旋极化曲线随入射能量的增加而振荡衰减;随着磁台阶数的增加,电子传输概率的自旋极化度最大值减小,同时电子传输概率的自旋极化度振荡衰减也越来越慢;随着磁台阶的总宽度增加,电子传输概率的自旋极化曲线出现更明显的振荡,电子隧穿磁台阶势垒表现出明显的量子尺寸效应;在偏置电压的作用下,电子传输概率的自旋极化度在宽广的入射能量区出现明显的振荡增大,电子隧穿磁台阶势垒表现出更明显的自旋过滤效应. 关键词： 磁台阶势垒 自旋极化 自旋过滤     

Spin polarization of electrons in magnetic heterostructures

The scattering of nonspin-polarized electrons on a heterostructure containing a magnetic element (a nonmagnetic barrier adjoining a magnetic one from left or right, or a magnetic well between two nonmagnetic barriers) is considered. The transmission coefficients and degrees of the spin polarization of electrons transmitted through these structures are obtained.     

量子自旋液体的实验研究进展

量子自旋液体是指由于其中存在的强量子涨落导致自旋即使在零温极限下也不形成磁有序的一种新的自旋量子态。区别于传统的磁有序材料,它的基态没有确定的序参量来表示,并且不伴随任何自发的对称性破缺,超越了朗道相变理论所能描述的物相范畴,代表了一种新奇的量子物态,具有非常高的理论研究价值。这一全新的物态被认为与非常规超导机制之间有着十分紧密的关系。同时在未来的量子计算方面有着非常诱人的应用前景,因此一直以来备受关注。虽然量子自旋液体理论经过近半个世纪的积淀有了长足的发展,但是由于候选材料稀少,实验测量条件苛刻等多种因素制约,导致实验方面的进展相对缓慢。近年来各项实验技术的进步和成熟为量子自旋液体候选材料的测量表征提供了有利条件,加快了实验工作的推进速度。本文将从实验的角度介绍 (1) 几何阻挫量子自旋液体候选材料,包括三角晶格化合物 YbMgGaO量子自旋液体是指由于其中存在的强量子涨落导致自旋即使在零温极限下也不形成磁有序的一种新的自旋量子态。区别于传统的磁有序材料,它的基态没有确定的序参量来表示,并且不伴随任何自发的对称性破缺,超越了朗道相变理论所能描述的物相范畴,代表了一种新奇的量子物态,具有非常高的理论研究价值。这一全新的物态被认为与非常规超导机制之间有着十分紧密的关系。同时在未来的量子计算方面有着非常诱人的应用前景,因此一直以来备受关注。虽然量子自旋液体理论经过近半个世纪的积淀有了长足的发展,但是由于候选材料稀少,实验测量条件苛刻等多种因素制约,导致实验方面的进展相对缓慢。近年来各项实验技术的进步和成熟为量子自旋液体候选材料的测量表征提供了有利条件,加快了实验工作的推进速度。本文将从实验的角度介绍(1)几何阻挫量子自旋液体候选材料,包括三角晶格化合物YbMgGaO_4和YbZnGaO_4、κ-(BEDT-TTF)_2Cu_2(CN)_3、EtMe_3Sb[Pd(dmit)_2]_2和kagome格子化合物ZnCu_3(OH)_6Cl_2;(2)Kitaev量子自旋液体候选材料铱氧化物(Na_2IrO_3与α-,β-,γ-Li_2IrO_3)和α-RuCl_3。文章将着重介绍近年来在量子自旋液体实验方面的进展,之后做一个简单的总结,最后对量子自旋液体的未来发展做一个展望。     

Spin Splitting in Different Semiconductor Quantum Wells

We theoretically investigate the spin splitting in four undoped asymmetric quantum wells in the absence of external electric field and magnetic field. The quantum well geometry dependence of spin splitting is studied with the Rashba and the Dresselhaus spin-orbit coupling included. The results show that the structure of quantum well plays an important role in spin splitting. The Rashba and the Dresselhaus spin splitting in four asymmetric quantum wells are quite different. The origin of the distinction is discussed in this work.     

自旋光电流与电流诱导的电子自旋极化——半导体自旋电子学的新进展

文章通过自旋光电流与Kerr效应的实验，介绍在自旋一轨道耦合的体系中，如何通过自旋注入来驱动电子的运动产生电流，又如何反过来通过电子的运动或电流在系统中产生自旋激化．实验结果表明，自旋轨道耦合不但给我们提供了对自旋的操控手段，而且还给我们提供了用非磁性材料且无外加磁场条件下作为自旋源的新途径．     

Spin polarization transitions in the FQHE

The spin polarization of the FQHE ground states at fixed filling factors is analyzed within a composite fermion model. As a function of the perpendicular magnetic field several cross‐overs between differently polarized ground states are predicted, in agreement with recent experimental investigations. The magnetic field and temperature scalings of the polarization, as well as the magnetic field dependence of the spin‐flip gap are studied.     

Spin current in double quantum dot

We have studied the dynamical behaviours of two electrons confined in a double quantum dot driven by rotating magnetic fields in terms of the theory of Lewis－Riesenfeld Hermitian invariants for the explicitly time-dependent Hamiltonian. The coherent spin oscillations in the dot provide a generation source for spin current. Exact solutions obtained allow us to investigate the dynamical properties of the spin localization for various initial localized states.