半导体自旋霍尔效应与石墨烯一维零线模态研究

发布时间：2018-06-25 01:42

本文选题：自旋霍尔效应 + 立方Rashba自旋轨道耦合　；参考：《中国科学技术大学》2017年博士论文

【摘要】：自旋霍尔效应是指纵向电流诱导产生横向自旋输运的一种现象。作为自旋电子学领域的重要概念和方法,自旋霍尔效应提供了利用纯电学手段来操控自旋自由度的可能。根据自旋轨道耦合来源的不同,自旋霍尔效应的产生机制分为内禀性和外禀性两种,其中外禀性机制中又包含侧跃(side jump)和偏散射(skew scattering)两种效应。自2003年以来,关于半导体材料中自旋霍尔效应的微观动力学研究已经取得了很大的进展,各机制单独作用下自旋霍尔效应的规律基本为人们所掌握,计算得到的自旋霍尔电导与实验定量符合。另一方面,内禀性与外禀性机制之间的关系与相互作用仍然有待厘清。在简单梳理各单一机制贡献的基础上,我们从量子刘维方程出发,得到弱散射情形下密度矩阵满足的动力学方程,方程中的哈密顿量将同时包含能带自旋轨道耦合和杂质自旋轨道耦合。经过计算,我们发现常规定义下的侧跃项和偏散射项对自旋霍尔效应贡献为零,系统另外出现与反常位置算符r_(SO)相关的两种反常自旋进动项,对于二维半导体电子体系,由电子反常进动项导致的自旋霍尔电导σ_(Eλ)~(SH)大小为纯侧跃霍尔电导的一半,而符号却与之相反。进一步地,我们将电子能带自旋轨道耦合由线性k项推广至立方Rashba项,对于前者,杂质反常自旋进动贡献σ_(Uλ)~(SH) =-σ_(Eλ)~(SH)的自旋霍尔电导,总自旋霍尔电导因此消失:对于后者,杂质反常自旋进动的贡献为σ_(Uλ)~(SH)=-σ_(Eλ)~(SH)/2,总自旋霍尔电导取有限值。反常自旋进动对空穴系统的贡献为零。反常自旋进动的出现,本质上可视为电场和杂质相关的自旋轨道耦合对能带自旋轨道耦合的重整化效应。最后,我们认为有希望在二维锑化铟量子阱体系中观察到反常自旋进动霍尔效应。相比传统半导体材料,石墨烯具有单原子层厚的本征二维属性和低能线性色散关系,堪称孕育新奇量子物态的温床。基于石墨烯的(量子)自旋霍尔效应,(量子)谷霍尔效应和(量子)反常霍尔效应等理论方案相继被提出。石墨烯动量空间中的两能谷相距较远,谷间散射较弱,低能下谷指标作为赝自旋自由度,可以用于电子学信息处理。在空间反演对称破缺的情况下,石墨烯中将出现谷霍尔效应现象,与自旋霍尔效应类似,这时纵向电场将导致不同能谷处的电子偏向样品相反边界,产生谷指标的横向传递。双层石墨烯的空间反演对称性能够被外加层间电势差所破坏,在此基础上,当层间电势差在空间某处发生翻转,翻转处会出现局域的一维零线模态。零线模态与翻转势两侧区域的能带拓扑性质有关并受到拓扑保护。零线模态携带确定的谷指标,其传输方向呈现手征性,可以被用来设计和操控电流通道。双层石墨烯层间电势差的最直接实现方案是利用外电极加压,由于零线模态所允许的翻转势的最大跨度在100mm以内。不同极板之间的准直会对一维零线模态的实验观察产生显著的影响。我们考虑了外电极的各种可能空间几何位错,并利用紧束缚模型方法模拟了各种位错对零线模态能带的影响。我们发现上下极板之间的相对位移对零线模态能带的扭曲为最大,而零线模态传输方向对石墨烯晶格周期类型的依赖并不敏感。考虑到实际样品中广泛存在各种拓扑缺陷,我们利用Landauer-Buttiker公式计算了拓扑缺陷对零线模态输运性质的影响,结果证明零线模态具有较强的鲁棒性。我们希望该项研究能够对实验提供一定指导意义。
[Abstract]:The spin Holzer effect is a phenomenon of transverse spin transport induced by longitudinal current. As an important concept and method in the field of spintronics, the spin Holzer effect provides the possibility of manipulating spin freedom by means of pure electrical means. The mechanism of the spin Holzer effect is divided into a mechanism based on the difference of the source of spin orbit coupling. There are two kinds of natural and natural nature, of which there are two effects in the intrinsic mechanism, which are side jump (side jump) and partial scattering (skew scattering). Since 2003, a great progress has been made in the study of the micro dynamics of the spin Holzer effect in semiconductor materials. The rules of the spin Holzer effect under the individual mechanisms of each mechanism are basically the people. On the other hand, the relationship and interaction between the intrinsic and the intrinsic mechanism remains to be clarified. On the basis of the simple combing of the contribution of each single mechanism, we start from the quantum Liu Wei equation to obtain the kinetic equation that the density matrix satisfies in the case of weak scattering. The Hamiltonian in the equation will include both the spin orbit coupling and the impurity spin orbit coupling. After calculation, we find that the side jump and partial scattering term under the conventional definition contribute zero to the spin Holzer effect, and the system also has two anomalous spin precession related to the anomalous position operator r_ (SO), for two-dimensional semiconductor electricity. The spin Holzer conductance (E lambda) ~ (SH) is the half of the pure side jump Holzer conductance caused by the electronic anomalous precession term, and the symbol is the opposite. Further, we extend the spin orbit coupling from the linear K term to the cubic Rashba term. For the former, the impurity anomalous spin precession contributes sigma (SH) = - Sigma (E lambda) ~ (S) ~ (S) H's spin Holzer conductance, the total spin Holzer conductance is disappearing: for the latter, the contribution of the impurity anomalous spin precession is the sigma (U lambda) ~ (SH) = ~ (E lambda) ~ (SH) /2, the total spin Holzer conductance limited. The anomalous spin precession has a zero contribution to the cavitation system. The appearance of the anomalous spin precession is essentially regarded as the electric field and the spin related spin. The renormalization effect of the orbital coupling on the coupled spin orbit coupling. Finally, we believe that there is a hope to observe the anomalous spin precession Holzer effect in the two-dimensional indium quantum well system. Compared with the traditional semiconductor materials, the graphene has the intrinsic two-dimensional properties of the single atomic layer and the low energy linear dispersion relation, which can be known as a novel quantum state. The theoretical schemes based on the (quantum) spin Holzer effect of graphene, the (quantum) Valley Holzer effect and the (quantum) anomalous Holzer effect have been proposed. The two energy valleys in the momentum space of the graphene are far apart, the inter Valley scattering is weak, and the low energy valley index as a pseudo self rotation freedom can be used in the electronic information processing. The spatial inversion can be used in space inversion. In the case of symmetry breaking, the phenomenon of the valley Holzer effect will appear in graphene, similar to the spin Holzer effect, when the longitudinal electric field will lead to the electrons in different valleys at the opposite boundary and produce the transverse transfer of the valley index. The spatial inversion of the double graphene is destroyed by the interlayer potential difference. When the interlayer potential difference occurs somewhere in the space, there will be a local one-dimensional zero line mode. The zero line mode is related to the topological properties of the energy band on both sides of the flipping potential and is protected by the topology. The zero line mode carries the definite Valley index, and its transmission direction is chiral, which can be used to design and manipulate the double layer stone. The most direct way to realize the potential difference between the laminar layer is to use the external electrode pressure, because the maximum span allowed by the zero line mode is within 100mm. The collimation between the different plates will have a significant effect on the experimental observation of the one-dimensional zero line mode. We find that the relative displacement between the upper and lower plates has the greatest distortion of the zero line modal energy band, and the zero line modal transmission direction is not sensitive to the dependence of the periodic type of the graphene lattice. Considering the wide variety of topological defects in the actual sample, we benefit. The effects of topological defects on the transport properties of zero line modal transport are calculated by the Landauer-Buttiker formula. The results show that the zero line mode has strong robustness. We hope that the study can provide some guidance for the experiment.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O469

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