拓扑材料中拓扑量子相变和输运性质的研究

发布时间：2018-01-01 16:43

本文关键词：拓扑材料中拓扑量子相变和输运性质的研究　出处：《南京大学》2017年博士论文　论文类型：学位论文

【摘要】：拓扑绝缘体是一种新奇的物质的态,它们的体能带与普通绝缘体一样存在能隙,但在边界处存在无能隙的边界态,这是由其能带结构的非平庸拓扑性质决定的。拓扑绝缘体由拓扑不变量Z2或自旋陈数来刻画。它的边界态由能带拓扑性和时间反演对称性所保护,因此不被非磁杂质散射,另外,边界态还具有螺旋结构,即动量和自旋是绑定的,这些性质在自旋电子学领域有广泛的应用。拓扑绝缘体在理论预言后不久,就在实验上被证实,并被推广到三维系统。它的迅速发展吸引的广泛的兴趣。受拓扑绝缘体的启发,人们将能带结构的分类扩展到了另一个方向——包括晶格对称性,并称这类由晶格对称性保护的拓扑绝缘体为“拓扑晶态绝缘体”。人们还预言了存在拓扑晶态绝缘相的真实材料,相关预言已被实验证实。另外,在二维蜂房格子系统中除了电荷自由度和自旋自由度,还存在着谷自由度,最近很多与谷相关的拓扑相变已经在理论上提出来了,利用这些谷相关的拓扑相,人们还设计了有趣的电子器件。在第二章中,我们讨论了在Zeeman场下拓扑晶态绝缘体SnTe表面态的拓扑性质。发现通过调节Zeeman场的方向,可以实现谷相关的拓扑相变。用赝自旋陈数描写系统的拓扑性质,我们得到半径为B的相球,其中包含陈数C=2的量子反常霍尔态,陈数C=1的量子反常霍尔态,量子赝自旋霍尔态,以及平庸拓扑绝缘体态。在C=1量子反常霍尔态和平庸绝缘体态中,两个谷处于不同的拓扑态。这种谷相关的拓扑相为设计低耗散的电子学器件以及基于拓扑晶态绝缘体的谷电子学应用提供了新的平台。拓扑绝缘体由拓扑不变量Z2指标或自旋陈数来刻画。然而,不同于描写量子霍尔效应的第一类陈数,到目前为止,这些拓扑不变量还未被直接测量和利用,虽然有几个方案已经提出来去观察它们。所以,测量这些拓扑不变量的更简单实用方法是值得期待的。在第三章,我们提出在硅烯中的拓扑泵浦效应,以直接测量系统的拓扑不变量。我们考虑在硅烯中施加两个含时电场,其中一个交变电场处于硅原子所在平面内,大小为Ey,另一个电场垂直平面,包含两部分,静电场和交变场,大小分别为E0z和E1z。使用自旋-谷陈数特征系统的拓扑性质,我们可以看到这个系统可以处于纯的谷泵浦态,混合的自旋-谷泵浦态,以及平庸泵浦态,由垂直电场的强度E0z和E1z决定。由散射矩阵计算的每个循环泵浦的谷和自旋总量与自旋-谷陈数描写完全一致。这个总量正比于样品的宽度,对材料参数不敏感,这说明了泵浦是一种体效应,与边缘态无关。自旋霍尔效应是由于自旋-轨道耦合,电荷流引起横向自旋流的物理现象。这种效应为产生自旋流提供了一种电学方法。基于相同的物理机制,纯自旋流也可以产生横向电荷流或可测量的电势差,这称为逆自旋霍尔效应。在第四章,我们发展了一套理论来描写Bi2Se3薄膜表面态的逆自旋霍尔效应。我们将Bi2Se3连接到电子库,对电子库施加自旋偏压,自旋偏压通过它在通道本征态子空间的投影驱动电子输运。我们说明了拓扑表面态是逆自旋霍尔效应的理想平台,由于拓扑绝缘体表面态的自旋-动量绑定,这里自旋偏压完全可以转换为可测量的横向电压,使拓扑绝缘体内纵向自旋流为零。我们的理论解释了实验上在拓扑绝缘体内观察到的大自旋霍尔角。此外,完美的逆Edelstein效应,即完整的自旋-电荷转换也可发生在表面态。在本文的最后一章,我们做了一个简单的总结和展望。
[Abstract]:Topological insulator is a kind of novel material state, and there exists a gap in their ordinary insulator as the Fitness Zone, but there are gapless boundary state at the boundary, which is decided by the non trivial topological properties of its band structure. The topological invariants of topological insulator Z2 or spin numbers to describe boundary state it. Chen the band topology and time reversal symmetry protection, and therefore is not a nonmagnetic impurity scattering, in addition, the boundary state also has spiral structure, namely momentum and spin is bound, these properties have been widely applied in the field of spintronics. Topological insulator shortly after the theoretical prediction is confirmed in. In experiment, and was extended to three-dimensional system. Its rapid development attracted wide interest. Inspired by the topological insulator, the classification of the band structure of people will extend to another direction, including the lattice symmetry, and called it by Topological insulator lattice symmetry protection "topological crystalline insulator". People also predicted the existence of amorphous insulating material phase real topology, the relevant predictions have been experimentally verified. In addition, in the two-dimensional honeycomb lattice system in addition to the degrees of freedom of charge and spin degrees of freedom, there are still many degrees of freedom and the valley, the valley recently in the theory of topological phase has been proposed, using the topology corresponding to the valley, people also design interesting electronic devices. In the second chapter, we discuss the Zeeman in the field of topological insulator amorphous surface states of SnTe topological properties. By adjusting the Zeeman field direction, can achieve Valley topological phase correlation the description of topological properties of systems with pseudo spin Chen Shu, we obtain the radius of ball B, which contains the quantum anomalous Holzer state Chen Shu C=2, Holzer Chen Shu C=1 state quantum anomalous, quantum pseudo self Holzer spin state, and the insulating body. Trivial topology in C=1 quantum anomalous Holzer state and mediocre insulation posture, two in the valley. The valley of different topological state related topological phase for electronics design and application of low dissipation valleytronics amorphous insulator based on topology provides a new platform to characterize topological insulators. A topological invariant Z2 index or spin Chen Shu. However, different from the first class Chen Shu description of quantum Holzer effect, so far, these topological invariants have not been directly measured and utilized, although several solutions have been proposed to observe them. Therefore, more simple and practical method for measuring these topological invariants is worth looking forward to. The third chapter, we propose the topology in the pump effect of silylenes, with topological invariants of a direct measurement system. We consider two applied time-dependent electric field in silylenes, one of the An alternating electric field in silicon atoms within the plane, vertical plane size is Ey, another electric field, consists of two parts, electrostatic field and magnetic field, the size of topological properties of E0z and E1z. using spin - Chen Shu Valley features of the system, we can see that this system can be in the valley of pumped state pure, mixed spin the valley - pumped state and mediocre pumped state by the vertical electric field strength of E0z and E1z. Each cycle pump is calculated from the scattering matrix of the valley and the total spin and spin Valley Chen Shu describes exactly the same. The total amount is proportional to the width of the sample, is not sensitive to the material parameters, which indicates that the pump is a kind of body the effect that has nothing to do with the edge state. The Holzer effect is due to the spin spin orbit coupling, charge flow caused by the physical phenomenon of transverse spin flow. This effect provides a method for producing electrical spin current based on the same physical mechanism, Pure spin can also produce potential lateral charge flow or can be measured, which is called the inverse spin Holzer effect. In the fourth chapter, the inverse spin Holzer effect, we develop a theory to describe the surface state of Bi2Se3 thin films. We connect the Bi2Se3 to the electronic library, electronic, and spin spin bias, bias drive the electron transport in the eigenstates of the subspace projection channel through it. We show that the topological state is an ideal platform for the inverse Holzer effect due to spin, spin momentum topological insulator surface state binding, here the spin bias can be converted to a completely transverse voltage can be measured, the topological insulator longitudinal spin current is zero our theory explains the experimental topology in the insulation of large spin Holzer observed in vivo angle. In addition, inverse Edelstein effect is perfect, i.e. complete spin charge transfer can also occur in the surface state in this paper. In the last chapter, we have made a simple summary and prospect.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O469

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