Liu Cheng-Cheng, Zhou Jin-Jian, Yao Yugui, Zhang Fan
Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA.
School of Physics, Beijing Institute of Technology, Beijing 100081, China.
Phys Rev Lett. 2016 Feb 12;116(6):066801. doi: 10.1103/PhysRevLett.116.066801. Epub 2016 Feb 9.
While strong topological insulators (STIs) were experimentally realized soon after they were theoretically predicted, a weak topological insulator (WTI) has yet to be unambiguously confirmed. A major obstacle is the lack of distinct natural cleavage surfaces to test the surface selective hallmark of a WTI. With a new scheme, we discover that β-Bi4X4 (X=Br, I), dynamically stable or synthesized before, can be a prototype WTI with two natural cleavage surfaces, where two anisotropic Dirac cones stabilize and annihilate, respectively. We further find four surface-state Lifshitz transitions under charge doping and two bulk topological phase transitions under uniaxial strain. Near the WTI-STI transition, there emerges a novel Weyl semimetal phase, in which the Fermi arcs generically appear at both cleavage surfaces whereas the Fermi circle only appears at one selected surface.
虽然强拓扑绝缘体（STIs）在理论预测后不久就通过实验实现了，但弱拓扑绝缘体（WTI）尚未得到明确证实。一个主要障碍是缺乏清晰的天然解理面来测试WTI的表面选择性特征。通过一种新方案，我们发现之前动态稳定或合成的β-Bi4X4（X = Br，I）可以成为具有两个天然解理面的WTI原型，其中两个各向异性的狄拉克锥分别稳定和湮灭。我们进一步发现在电荷掺杂下有四个表面态里夫希茨转变，在单轴应变下有两个体拓扑相变。在WTI-STI转变附近，出现了一种新型的外尔半金属相，其中费米弧通常出现在两个解理面上，而费米面只出现在一个选定的表面上。
