$(Bi_{1-x}In_x)_2 Se_3$拓扑相变中输运寿命的突然崩塌
A sudden collapse in the transport lifetime across the topological phase transition in $(Bi_{1-x}In_x)_2 Se_3$
摘要：
拓扑绝缘体（TI）是一种新发现的物质态，它具有由体波函数拓扑性质所保护的坚固的金属表面态。从TI到常规绝缘体的量子相变（QPT）和拓扑类的变化仅在体带隙关闭时才能发生。在这项工作中，我们已经利用时域太赫兹光谱（THEMS），以调查（Bi $_{1-x}$ In $_x$）$_2$ Se $_3$的低频电导，因为我们通过铟替代这个过渡调谐。在一定的替代水平以上，我们观察到的运输寿命，这表明拓扑相的破坏崩溃。我们将这种效应与来自相反表面的状态杂交的阈值相关联。阈值的取代水平取决于厚度，并且仅渐近地接近本体极限$x \approx 0.06$，其中在中红外吸收中表现出最大值。这种吸收可以用体带隙闭合和拓扑类的变化来识别。与QPT相关的相关长度表现为表面态的倏逝长度。的厚度依赖的崩溃的运输寿命的观察显示了不寻常的作用，有限尺寸效应在这个拓扑QPT。
英文摘要：
Topological insulators (TIs) are newly discovered states of matter with robust metallic surface states protected by the topological properties of the bulk wavefunctions. A quantum phase transition (QPT) from a TI to a conventional insulator and a change in topological class can only occur when the bulk band gap closes. In this work, we have utilized time-domain terahertz spectroscopy (TDTS) to investigate the low frequency conductance in (Bi$_{1-x}$In$_x$)$_2$Se$_3$ as we tune through this transition by indium substitution. Above certain substitution levels we observe a collapse in the transport lifetime that indicates the destruction of the topological phase. We associate this effect with the threshold where states from opposite surfaces hybridize. The substitution level of the threshold is thickness dependent and only asymptotically approaches the bulk limit $x \approx 0.06$ where a maximum in the mid-infrared absorption is exhibited. This absorption can be identified with the bulk band gap closing and a change in topological class. The correlation length associated with the QPT appears as the evanescent length of the surface states. The observation of the thickness-dependent collapse of the transport lifetime shows the unusual role that finite size effects play in this topological QPT.
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