铁磁、肖特基金属和半导体纳米自旋过滤器中的量子尺寸效应

采用转移矩阵法,研究了结构尺度对自旋过滤器中电子自旋极化特性的影响．该自旋过滤器可以通过在半导体异质结上沉积纳米尺度的铁磁条带和肖特基金属条带来实现．计算结果表明,电子的自旋极化特性强烈依赖于铁磁条带和肖特基金属条带的结构尺度和位置,即该器件中存在量子尺寸效应．此外,我们的计算结果还表明,电子的自旋极化特性还与施加在肖特基金属条上的电压所诱发的电垒高度密切相关．因此,我们可以通过改变施加在肖特基金属条上的电压来调控该器件中电子的自旋极化特性,制造一个电压可调的电子自旋过滤器．     

纳米金属膜的量子尺寸效应

当金属结构的几何尺寸小到纳米量级,例如,跟相应的电子费密波长（Fermi wavelength）可比时,由于量子约束效果已变得非常明显,该金属纳米结构经常会呈现出尺寸依赖的物理特征。这种现象被称作“量子尺寸效应（Quantum size effect,QSE）”。而对于大块金属晶体,正如我们熟知的,其物理特征与几何尺寸是没有依赖关系的。这说明金属纳米结构跟相应的大块金属晶体的性质是很不相同的。     

有机铁磁界面自旋极化接触构型效应

基于第一性原理,研究了三种不同的接触构型垂直吸附在镍表面的苯双硫分子的界面自旋极化.结果表明界面自旋极化强烈依赖于接触构型,接触构型的变化可使自旋极化由正值变为负值.通过分析投影态密度,发现界面处镍原子的3d轨道与硫原子的sp³杂化轨道发生了轨道杂化.模拟机械可控断裂结实验中的界面吸附构型,根据计算的界面自旋极化,利用Julliere模型得到磁电阻约为27%,与实验测量结果较为符合.     

铁磁石墨烯体系的CT不变量子自旋霍尔效应

文章作者在垂直磁场作用下的铁磁石墨烯体系里预言了一种新类型的量子自旋霍尔效应.这量子自旋霍尔效应与自旋轨道耦合无关,体系也不具有时间反演不变性;但是有CT不变（C为电子-空穴变换、T为时间反演变换）.由于量子自旋霍尔效应,体系的纵向电阻和自旋霍尔阻出现量子化平台.特别是,自旋霍尔阻的量子化平台有很强的抗杂质干扰能力.     

超微半导体AgBr的量子尺寸效应

本文研究了间接带半导体ＡｇＢｒ由于空间尺寸的限制产生的吸收，荧光兰移，激子振子强度增强的量子尺寸效应，观察到旋－轨道分裂带至导带的２８４ｎｍ吸收峰，经硫处理的Ａｇｂｒ直接激子吸收峰从３１０ｎｍ移至３０１ｎｍ。相应的荧光从３４０ｎｍ移至３２４ｎｍ，同时在８５０ｎｍ处产生了一新的荧光带。     

铁磁石墨烯体系的CT不变量子自旋霍尔效应

文章作者在垂直磁场作用下的铁磁石墨烯体系里预言了一种新类型的量子自旋霍尔效应.这量子自旋霍尔效应与自旋轨道耦合无关,体系也不具有时间反演不变性;但是有CT不变(C为电子-空穴变换、T为时间反演变换).由于量子自旋霍尔效应,体系的纵向电阻和自旋霍尔阻出现量子化平台.特别是,自旋霍尔阻的量子化平台有很强的抗杂质干扰能力.     

自旋Seebeck效应简介

自旋电子学作为一个新兴的学科,是未来电子学发展的重要方向之一.而近年来发现的自旋泽贝克（Seebeck）效应则为自旋电子学的研究提供了不少新现象.文章通过对自旋Seebeck效应的一些科研进展的介绍,较详尽地阐明了自旋Seebeck效应的定义和常用的利用逆自旋霍尔（Hall）效应来进行观测的机制与方法,并对不同种类材料中的自旋Seebeck效应及其可能的成因进行了分析介绍.     

量子材料中的自旋—动量锁定新效应

继铁磁金属之后,具有强自旋轨道耦合与空间反演破缺的自旋极化量子材料,通过自旋—动量锁定（如Rashba、Dresselhaus自旋劈裂）,实现了如自旋轨道矩、自旋场效应晶体管等新一代自旋电子学效应。近期,通过耦合新自由度,研究者们发现了一些新奇的自旋—动量锁定效应,包括突破空间反演对称限制的“隐藏自旋极化”效应和突破自旋轨道耦合限制的“反铁磁自旋极化”效应,这些发现再一次拓宽了可利用的自旋电子学材料。文章简要回顾了自旋—动量锁定效应的基本原理和发展现状,重点介绍了耦合实空间自由度的自旋—动量—层锁定效应,即隐藏自旋极化;和耦合局域磁矩自由度产生的与自旋轨道耦合无关的自旋—动量锁定效应,即反铁磁自旋极化;以及与两者相关的新型自旋电子学效应。最后,展望了自旋—动量锁定中多自由度耦合问题、隐藏X物理和反铁磁自旋电子学三个方面的未来发展。     

磁量子结构中二维自旋电子的隧穿输运

研究了零偏压和偏置电压作用下磁量子结构中自旋电子的隧穿输运性质. 结果表明电子自旋 输运的性质不仅取决于磁量子结构的构型、入射电子的能量和波矢, 而且取决于偏置电压. 在零偏压下, 由等同的磁垒磁阱构成的磁量子结构不具有自旋过滤的特点, 而由不等同的磁 垒磁阱构成的磁量子结构却具有较好的自旋过滤特点. 偏置电压极大地改变了磁量子结构中 电子的极化程度, 使得电子隧穿等同的磁垒磁阱构成的磁量子结构的输运性质也显著地依赖 于电子的自旋指向. 关键词： 磁量子结构 自旋电子 隧穿输运 自旋极化     

相互作用量子点的自旋相关输运

介绍了与磁性电极耦合的量子点的近藤共振、单电子能级自旋劈裂、磁化和线性电导等物理性质．研究结果显示，当磁性电极磁矩取向相同的时候，线性电导在低温下呈现双峰结构．而近藤共振和单电子能级的自旋劈裂都可以通过电极的内部磁化强度来控制，可以用来产生自旋阀效应．     

A bias-tunable electron-spin filter based on a hybrid ferromagnetic-Schottky-metal and semiconductor nanostructure

Recently, an electron-spin filter was proposed by depositing two ferromagnetic stripes and a Schottky normal-metal stripe on top of a heterostructure [H.Z. Xu, Q.Q. Yan, Phys. Lett. A 372 (2008) 6216]. Here, we apply a bias to this device, and find that both magnitude and sign of the electron-spin polarization are sensitive to the applied bias, which can result in a bias-tunable spin filter.     

Size- and voltage-dependent spin polarization in hybrid ferromagnetic-Schottky-metal and semiconductor nanostructure

Recently, an electron-spin filter was proposed by depositing two nanosized ferromagnetic metal stripe and Schottky normal metal stripe on the top of the semiconductor heterostructure [F. Zhai, H.Q. Xu, Y.Guo, Phys. Rev. B 70 (2004) 085308]. In this paper, we theoretically investigate the effect of device parameters on electron-spin polarization in the spin filter. It is shown that the electron-spin polarization is dependent greatly on the sizes and the position of the stripes. Thus, a quantum size effect exists in this device and the optimal spin polarization can be achieved by felicitously fabricating the stripes. It also is shown that the spin polarization can be altered by adjusting the electric-barrier height induced by an applied voltage to the Schottky metal stripe, which can result in a voltage-tunable electron-spin filter.     

Giant magnetoresistance effect in hybrid ferromagnetic-Schottky-metal and semiconductor nanosystem

We report on a theoretical investigation of the giant magnetoresistance (GMR) effect in hybrid ferromagnetic-Schottky-metal and semiconductor nanosystem. Experimentally, this GMR device can be realized by the deposition of two ferromagnetic (FM) stripes and one Schottky normal metal (NM) in parallel way on the top of a semiconductor GaAs heterostructure. The GMR effect emanates from the significant transmission difference for electrons tunneling through parallel and antiparallel magnetization configurations of the device, and its magnetoresistance ratio (MR) can reach the order of ¹⁰⁶%. Furthermore, it is also shown that the MR of the device depends strongly on the relative location of the Schottky NM stripe between two FM stripes.     

Magnetoresistance effect in a hybrid ferromagnetic/semiconductor nanostructure

We propose a Magnetoresistance device in a magnetically modulated two-dimensional electron gas, which can be realized experimentally by the deposition of two parallel ferromagnetic strips on the top and bottom of a semiconductor heterostructure. It is shown that there exists a significant transmission difference for electrons through the parallel and antiparallel magnetization configurations of such a device, which leads to a considerable magnetoresistance effect. It is also shown that the magnetoresistance ratio of the device depends greatly on the magnetic strength difference in the two delta barriers of the system.     

Converting Wannier into Frenkel excitons in an inorganic/organic hybrid semiconductor nanostructure

Electronic coupling between Wannier and Frenkel excitons in an inorganic/organic semiconductor hybrid structure is experimentally observed. Time-resolved photoluminescence and excitation spectroscopy directly demonstrate that electronic excitation energy can be transferred with an efficiency of up to 50% from an inorganic ZnO quantum well to an organic [2,2-p-phenylenebis-(5-phenyloxazol), alpha-sexithiophene] overlayer. The coupling is mediated via dipole-dipole-interaction analog to the F?rster transfer in donor-acceptor systems.     

Spontaneous spin polarization in doped semiconductor quantum wells

We calculate the critical density of the zero-temperature, first-order ferromagnetic phase transition in n-doped GaAs/AlGaAs quantum wells. We predict that this transition could be observed in narrow quantum wells at electron densities somewhat lower than the ones that have been considered experimentally thus far, and that there exists an upper limit for the well width beyond which there would be no transition as long as only one subband is populated. Our calculations are done within a screened Hartree-Fock approximation with a polarization-dependent effective mass, which is adjusted to match the critical density predicted by Monte Carlo calculations for the strictly two-dimensional electron gas.     

超构材料中的光学量子自旋霍尔效应

电子的量子自旋霍尔效应的发现推进了当今凝聚态物理学的发展,它是一种电子自旋依赖的具有量子行为的输运效应.近年来,大量的理论和实验研究表明,描述电磁波场运动规律的麦克斯韦方程组内禀了光的量子自旋霍尔效应,存在于界面的倏逝波表现出强烈的自旋与动量关联性.得益于新兴的光学材料:超构材料(metamaterials)的发展,不仅能够任意设定光学参数,同时也能引入很多复杂的自旋-轨道耦合机理,让我们能够更加清晰地了解和验证其中的物理机理.本文对超构材料中量子自旋霍尔效应做了简要的介绍,内容主要包括真空中光的量子自旋霍尔效应的物理本质、电单负和磁单负超构材料能带反转导致的不同拓扑相的界面态、拓扑电路系统中光量子自旋霍尔效应等.     

High-speed all-optical differentiator based on a semiconductor optical amplifier and an optical filter

We demonstrate a novel all-optical differentiator that carries out the first-order temporal derivation of optical intensity variation at high speed. It consists of a semiconductor optical amplifier (SOA) and an optical filter (OF) serving as an optical phase modulator and a frequency discriminator, respectively. A polarity-reversed derivative pair with a certain bias can be obtained by locating the probe wavelength at the positive or negative slope of the OF. Differentiations of super-Gaussian and Gaussian signals are obtained at various data rates. Defined as the mean absolute deviation of the measured result from the ideal result, total average errors of less than 0.12 are observed in all cases. Input power dynamics as well as control wavelength dependence are investigated and show that the cross-gain modulation in the SOA is detrimental to the differentiation performance.     

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．