拓扑绝缘体（TI）的一个关键特征是哈密顿量的辛对称性，当时间反演对称性被解除并且拓扑相变发生时，该辛对称性变为么正的。然而，这样的交叉从未被明确观察到，通过直接探测哈密顿量的对称类。在这份报告中，我们已经探讨了拓扑绝缘体的对称类通过测量介观电导波动的TI Bi $_{1.6}$ Sb $_{0:4}$ Te $_2$ Se，这表明了一个确切的因素减少应用的磁场由于交叉从辛到酉对称类。这一还原提供了一个明确的证据，即波动是由量子干涉引起的普适电导波动（UCF）引起的，并且从T = 22 mK持续到4.2 K。我们还比较了相位断裂长度（l $_ϕ$）提取的磁导率和UCF同意以及在整个温度和栅极电压范围内的两个因素。我们的实验证实了UCF是介观无序拓扑绝缘体中涨落的主要来源，以及这些系统中时间反演对称性的内在保持。
英文摘要：
A key feature of topological insulators (TI) is symplectic symmetry of the Hamiltonian which changes to unitary when time reversal symmetry is lifted and the topological phase transition occurs. However, such a crossover has never been explicitly observed, by directly probing the symmetry class of the Hamiltonian. In this report, we have probed the symmetry class of topological insulators by measuring the mesoscopic conductance fluctuations in the TI Bi$_{1.6}$Sb$_{0:4}$Te$_2$Se, which shows an exact factor of two reduction on application of a magnetic field due to crossover from symplectic to unitary symmetry classes. The reduction provides an unambiguous proof that the fluctuations arise from the universal conductance fluctuations (UCF), due to quantum interference and persists from T = 22 mK to 4.2 K. We have also compared the phase breaking length (l$_ϕ$) extracted from both magneto-conductivity and UCF which agree well within a factor of two in the entire temperature and gate voltage range. Our experiment confirms UCF as the major source of fluctuations in mesoscopic disordered topological insulators, and the intrinsic preservation of time reversal symmetry in these systems.
The quantized conductance plateaus and zero conductance fluctuation are the general consequence of electron transport in chiral edge states of Hermitian Chern insulators. Here we show that the physics of electron transport through chiral or helical edge channels becomes much richer when the non-Hermicity is allowed. In the presence of an unbalanced non-Hermicity where the chiral edge states have finite-lifetime, the conductance of the edge channels is not quantized, but its conductance fluctuation is zero. For the balanced non-Hermicity, however, the chiral edge states have infinite-lifetime, …
Recently,a half-quantized Hall conductance (HQHC) plateau is experimentally observed in a semi-magnetic topological insulator heterostructure. However,the heterostructure is metallic with a nonzero longitudinal conductance, which contradicts the common belief that quantized Hall conductance is usually observed in insulators.In this work,we systematically study the surface transport of the semi-magnetic topological insulator with both gapped and gapless Dirac surfaces in the presence of dephasing process.In particular, we reveal that the HQHC is directly related to the half-quantized chiral cur…
We investigate the Hall conductance of a two-dimensional Chern insulator coupled to an environment causing gain and loss. Introducing a biorthogonal linear response theory, we show that sufficiently strong gain and loss lead to a characteristic non-analytical contribution to the Hall conductance. Near its onset, this contribution exhibits a universal power-law with a power 3/2 as a function of Dirac mass, chemical potential and gain strength. Our results pave the way for the study of non-Hermitian topology in electronic transport experiments.
Anomalous Aharonov-Bohm conductance oscillations from topological insulator surface states
研究了拓扑绝缘体纳米线在沿其长度方向施加磁场时的输运性质。我们预测，与强表面无序，一个特征签名的带拓扑结构中透露的Aharonov玻姆（AB）振荡的电导。这些振荡具有异常周期$Φ_0=hc/e$的分量，并且在$\frac12Φ_0$的奇数倍处具有电导最大值，即当表面电子的AB相是$π$时。这与能带拓扑和表面曲率诱导的Berry相密切相关，特别是对于拓扑绝缘体表面。我们讨论了最近的实验上的Bi $_2$ Se $_3$纳米带的相似性和差异，并观察这种效果的最佳条件。
Magnetic insulators are promising materials for the development of energy-efficient spintronics. Unlike metallic counterparts, the magnetic insulators are characterized by imaginary part of the interfacial spin mixing conductance as well in a bilayer with heavy metals and it is responsible for the field-like toque in spin-orbit torque devices. Here, we study the underlying theoretical constructs and develop a general strategy to determine the complex spin mixing conductance from the experimental results of ferromagnetic resonance and spin pumping. The results show that the imaginary part of th…
Crossover of conductance and local density of states in a single-channel disordered quantum wire
计算了具有手征对称性的单沟道无序量子线在两种不同几何结构下的介观局域态密度的概率分布。提出了一种近似的解析法来描述单沟道无序量子线的电导和LDOS的概率分布在手征对称类和标准对称类之间的交叉。通过与Schomerus和Titov在Phys. Rev. B \textbf{67}，100201（R）（2003）中引入的大偏差分析法进行比较，讨论了该分析法的准确性。
We find the nonlinear conductance of a dissipative resonant level in the nonequilibrium steady state near its quantum critical point. The system consists of a spin-polarized quantum dot connected to two resistive leads that provide ohmic dissipation. We focus on the crossover from the strong-coupling, non-Fermi-liquid regime to the weak-coupling, Fermi-liquid ground state, a crossover driven by the instability of the quantum critical point to hybridization asymmetry or detuning of the level in the dot. We show that the crossover properties are given by tunneling through an effective single bar…
We consider the superconductor-semiconductor nanowire hybrid Majorana platform ("Majorana nanowire") in the presence of a deterministic spatially slowly varying inhomogeneous chemical potential and a random spatial quenched potential disorder, both of which are known to produce nontopological almost-zero-energy modes mimicking the theoretically predicted topological Majorana zero modes. We study the crossover among these mechanisms by calculating the tunnel conductance while varying the relative strength between inhomogeneous potential and random disorder in a controlled manner. We find that t…
Transport in topological insulators with bulk-surface coupling: Interference corrections and conductance fluctuations
出于实验困难，以生产拓扑绝缘体（TI）的Bi $_2$ Se $_3$家庭与纯表面态导电，我们研究的效果，体可以对低温输运性质的门控薄膜TI。特别是，我们专注于干扰校正，即弱本地化（WL）或弱反本地化（WAL），和电导波动（CFs）的基础上，一个有效的低能哈密顿量。利用图解微扰理论，我们首先分析了体和表面分别和随后讨论WL/WAL和CF时，隧道耦合的介绍。我们确定相关的软扩散模式的耦合系统，并使用这种见解，同时预测在各种参数制度的干扰校正和电导波动。结果强烈表明，这两个量的组合测量可以提供一个更好的理解的物理基础的低温运输过程中的薄TI膜与体表面耦合。
Giant universal conductance fluctuations in the antiferromagnetic topological insulator MnBi2Te4
Leibniz Institute for Solid State and Materials Research, IFW Dresden（德累斯顿IFW固体与材料研究所）；TU Dresden（德累斯顿工业大学）；Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；CNRS（法国国家科学研究中心）；CEA（法国原子能和替代能源委员会）；Technical University of Dortmund（多特蒙德工业大学）；Research Center ”Future Energy Materials and Systems”（未来能源材料与系统研究中心）；Laboratoire National des Champs Magnetiques Intenses LNCMI（强磁场国家实验室）
The interface between a ferro-/ferrimagnetic insulator and a normal metal can support spin currents polarized collinear with and perpendicular to the magnetization direction. The flow of angular momentum perpendicular to the magnetization direction ("transverse" spin current) takes place via spin torque and spin pumping. The flow of angular momentum collinear with the magnetization ("longitudinal" spin current) requires the excitation of magnons. In this article we extend the existing theory of longitudinal spin transport [Bender and Tserkovnyak, Phys. Rev. B 91, 140402(R) (2015)] in the zero-…
We study backscattering of electrons and conductance suppression in a helical edge channel in two-dimensional topological insulators with broken axial spin symmetry in the presence of nonmagnetic point defects that create bound states. In this system the tunneling coupling of the edge and bound states results in the formation of composite helical edge states in which all four partners of both Kramers pairs of the conventional helical edge states and bound states are mixed. The backscattering is considered as a result of inelastic two-particle scattering of electrons, which are in these composi…
