采用第一性原理方法研究了体拓扑绝缘体Bi 2Se 3和Bi 2 Te 3中拓扑保护表面态的能带色散和自旋织构.在这两种情况下，这些材料中强的自旋-轨道纠缠将表面态的自旋极化降低到~50%;这种降低在简单模型中是不存在的，但对基本上任何自旋电子学应用都有重要意义。我们提出了一种通过外加电场来控制拓扑绝缘体薄膜中与电荷电流相关的自旋极化的大小的方法。所提出的双栅极器件配置提供了新的可能性，电控制的自旋。
英文摘要：
We investigate the band dispersion and the spin texture of topologically protected surface states in the bulk topological insulators Bi2Se3 and Bi2Te3 by first-principles methods. Strong spin-orbit entanglement in these materials reduces the spin-polarization of the surface states to ~50% in both cases; this reduction is absent in simple models but of important implications to essentially any spintronic application. We propose a way of controlling the magnitude of spin polarization associated with a charge current in thin films of topological insulators by means of an external electric field. The proposed dual-gate device configuration provides new possibilities for electrical control of spin.
We report on the possibility to detect hinge spin polarization in magnetic topological insulators by resistance measurements. By implementing a three-dimensional model of magnetic topological insulators into a multi-terminal device with ferromagnetic contacts near the top surface, local spin features of the chiral edge modes are unveiled. We find local spin polarization at the hinges that inverts sign between top and bottom surfaces. At the opposite edge, the topological state with inverted spin polarization propagates in the reverse direction. Large resistance switch between forward and backw…
We study the spin polarization of the electrons on the surface of topological insulators under a dc electric field or a circularly polarized light by using Keldysh Green's function formalism. When a dc electric field $E_x \sim 10^{3} {\rm V/m}$ is applied, a spin polarization $<σ_{y}> \simeq 5.2 \times 10^{-8}{\rm Å^{-2}}$ is induced. Furthermore, we also find that a light illumination induces the out-of-plane component of the spin polarization as a result of the inverse Faraday effect. The magnitude of the spin polarization is proportional to the square of the lifetime $τ$ and $<σ_{z}> \simeq…
Current-induced spin polarization in topological insulator-graphene heterostructures
全电自旋电子学领域的进一步发展需要自旋输运通道与自旋注入器/发生器元件的成功集成。虽然随着石墨烯和相关2D材料的出现，高性能自旋通道材料是可用的，但纳米结构自旋发生器的使用仍然是一个主要挑战。对于后一个目的，特别有希望的是3D拓扑绝缘体，其2D表面态具有自旋-动量锁定的无质量狄拉克费米子。在这里，我们证明了自旋极化电流从拓扑绝缘体注入石墨烯，使其紧密耦合到一个超导Bi 2 Te 2Se纳米片内的范德华外延异质结构。自旋开关信号的大小与温度成反比，在~15 K的温度下都可以检测到。我们的研究结果确立了拓扑绝缘体作为自旋电子器件的未来组件，其中自旋操纵是通过纯电气手段实现的。
Transport Properties of Topological Insulators Films and Nanowires
近几年来，人们对拓扑绝缘体的研究和认识发展迅速。本文在简要总结了拓扑绝缘体的发展历史后，重点介绍了拓扑绝缘体薄膜和纳米线输运实验的最新进展。一些量子现象，包括弱反局域化，Aharonov玻姆效应和Shubnikov de Haas振荡，在这些纳米结构中观察到的描述。此外，超导邻近效应的电子输运证据，以及在拓扑绝缘体/超导体混合结构的异常电阻增强包括在内。
Mapping the chemical potential dependence of current-induced spin polarization in a topological insulator
我们报告了在拓扑绝缘体器件中电流诱导的表面电流自旋极化的电测量，其中体导电和表面导电的贡献可以通过电门来解开。该器件使用铁磁隧道结（坡莫合金/Al 2 O3）作为背栅（Bi，Sb）2 Te 3通道上的自旋检测器。我们观察到滞后电压信号的检测器铁磁体的磁化切换平行或反平行的自旋极化的表面电流。检测到的电压变化的幅度与（Bi，Sb）2 Te 3通道中施加的DC偏置电流成线性比例。由于化学势从体能带调谐到表面态能带，我们观察到静电门控范围内自旋相关电压的增强高达300%。使用一个简单的模型，我们提取的自旋极化附近的电荷中性（即狄拉克点）。
Angular momentum transport is one of the cornerstones of spintronics. Spin angular momentum is not only transported by mobile charge carriers, but also by the quantized excitations of the magnetic lattice in magnetically ordered systems. In this regard, magnetically ordered insulators provide a platform for magnon spin transport experiments without additional contributions from spin currents carried by mobile electrons. In combination with charge-to-spin current conversion processes in conductors with finite spin-orbit coupling it is possible to realize all-electrical magnon transport schemes …
Pseudo-ballistic transport in 3D topological insulator quantum wires
研究了无序三维拓扑绝缘体量子线中的量子电导涨落。实验和理论都揭示了介观导体中一种新的输运机制，即伪弹道输运，其弹道性质持续超过输运平均自由程，具有扩散输运的特征。由于准1D表面模式，其导致非通用电导波动，如在长且窄的Bi $_2$ Se $_3$纳米带中所观察到的。量子线中的自旋螺旋狄拉克费米子由于强的量子限制和弱的动量散射而在异常宽的能量范围内保持伪弹道性质。
The discovery of topologically protected boundary states in topological insulators opens a new avenue toward exploring novel transport phenomena. The one-way feature of boundary states against disorders and impurities prospects great potential in applications of electronic and classical wave devices. Particularly, for the 3D higher-order topological insulators, it can host hinge states, which allow the energy to transport along the hinge channels. However, the hinge states haveonly been observed along a single hinge, and a natural question arises: whether the hinge states can exist simultaneou…
Symmetries, quantum geometries and electronic correlations are among the most important ingredients of condensed matters, and lead to nontrivial phenomena in experiments, for example, non-reciprocal charge transport. Here we report the non-reciprocal charge transport in the intrinsic magnetic topological insulator MnBi2Te4. The current direction relevant resistance is observed at chiral edges, which is magnetically switchable, edge position sensitive and septuple layer number controllable. Applying gate voltage can effectively tune the non-reciprocal resistance. The observation and manipulatio…
Electrical detection of the spin polarization due to charge flow in the surface state of the topological insulator Bi_1.5 Sb_0.5 Te_1.7 Se_1.3
用全电学方法研究了三维拓扑绝缘体自旋非简并表面态中由电荷流引起的自旋极化。在块体绝缘拓扑绝缘体Bi 1.5 Sb 0.5 Te 1.7 Se 1.3（BSTS）中，电荷电流通过由Ni 80 Fe 20制成的铁磁电极注入/引出，并且不寻常的电流方向相关的磁电阻为自旋极化的出现提供了证据，该自旋极化导致BSTS/Ni 80 Fe 20界面处的自旋相关电阻。相比之下，我们对Bi 2Se 3的对照实验给出了无效结果。这些观测结果表明了费米能级控制对于拓扑绝缘体自旋极化电探测的重要性。
We experimentally investigate the effect of electron temperature on transport in the two-dimensional Dirac surface states of the three-dimensional topological insulator HgTe. We find that around the minimal conductivity point, where both electrons and holes are present, heating the carriers with a DC current results in a non-monotonic differential resistance of narrow channels. We show that the observed initial increase in resistance can be attributed to electron-hole scattering, while the decrease follows naturally from the change in Fermi energy of the charge carriers. Both effects are gover…
Magnon transport through a magnetic insulator can be controlled by current-biased heavy-metal gates that modulate the magnon conductivity via the magnon density. Here, we report nonlinear modulation effects in 10$\,$nm thick yttrium iron garnet (YIG) films. The modulation efficiency is larger than 40\%/mA. The spin transport signal at high DC current density (2.2$\times 10^{11}\,$A/m$^{2}$) saturates for a 400$\,$nm wide Pt gate, which indicates that even at high current levels a magnetic instability cannot be reached in spite of the high magnetic quality of the films.
Bilayer Heisenberg ferromagnetic insulators hold degenerate terahertz Dirac magnon modes associated with two opposite valleys of the hexagonal Brillouin zone. We show that this energy degeneracy can be removed by breaking of the inversion symmetry (I), leading to a topological magnon valley current. We show furthermore that this current leads to valley Seebeck effect for magnons and is thereby detectable. We perform calculations in the specific example of bilayer CrBr3, where I can be broken by electrostatic doping.
In the transport studies of topological insulators, microflakes exfoliated from bulk single crystals are often used because of the convenience in sample preparation and the accessibility to high carrier mobilities. Here, based on finite element analysis, we show that for the non-Hall-bar shaped topological insulator samples, the measured four-point resistances can be substantially modified by the sample geometry, bulk and surface resistivities, and magnetic field. Geometry correction factors must be introduced for accurately converting the four-point resistances to the longitudinal resistivity…
