Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russian Federation.
National Research University Higher School of Economics, Moscow 101000, Russian Federation.
Phys Rev Lett. 2019 Aug 2;123(5):056801. doi: 10.1103/PhysRevLett.123.056801.
Recent topological band theory distinguishes electronic band insulators with respect to various symmetries and topological invariants, most commonly, the time reversal symmetry and the Z_{2} invariant. The interface of two topologically distinct insulators hosts a unique class of electronic states-the helical states, which shortcut the gapped bulk and exhibit spin-momentum locking. The magic and so far elusive property of the helical electrons, known as topological protection, prevents them from coherent backscattering as long as the underlying symmetry is preserved. Here we present an experiment that brings to light the strength of topological protection in one-dimensional helical edge states of a Z_{2} quantum spin-Hall insulator in HgTe. At low temperatures, we observe the dramatic impact of a tiny magnetic field, which results in an exponential increase of the resistance accompanied by giant mesoscopic fluctuations and a gap opening. This textbook Anderson localization scenario emerges only upon the time-reversal symmetry breaking, bringing the first direct evidence of the topological protection strength in helical edge states.
最近的拓扑能带理论根据各种对称性和拓扑不变量来区分电子能带绝缘体，最常见的是时间反演对称性和 Z_{2}不变量。两个拓扑不同的绝缘体的界面上存在一类独特的电子态——螺旋态，它缩短了带隙体并表现出自旋-动量锁定。螺旋电子的神奇且迄今难以捉摸的特性，即拓扑保护，只要底层对称性得到保持，就可以防止它们相干背散射。在这里，我们进行了一项实验，揭示了 HgTe 中 Z_{2}量子自旋霍尔绝缘体一维螺旋边缘态中拓扑保护的强度。在低温下，我们观察到微小磁场的巨大影响，这导致电阻呈指数增长，同时伴随着巨大的介观涨落和能隙打开。这种教科书式的安德森局域化情景仅在时间反演对称性破坏时出现，这为螺旋边缘态中的拓扑保护强度提供了第一个直接证据。
