Department of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742-4111, USA.
Nat Commun. 2013;4:2040. doi: 10.1038/ncomms3040.
The two-dimensional surface of the three-dimensional topological insulator is in the symplectic universality class and should exhibit perfect weak antilocalization reflected in positive weak-field magneto-resistance. Previous studies in topological insulator thin films suffer from high level of bulk n-type doping making quantitative analysis of weak antilocalization difficult. Here we measure the magneto-resistance of bulk-insulating Bi2Se3 thin films as a function of film thickness and gate-tuned carrier density. For thick samples, the magnitude of weak antilocalization indicates two decoupled (top and bottom) symplectic surfaces. On reducing thickness, we observe first a crossover to a single symplectic channel, indicating coherent coupling of top and bottom surfaces via interlayer tunnelling, and second, a complete suppression of weak antilocalization. The first crossover is governed by the ratio of phase coherence time to the inter-surface tunnelling time, and the second crossover occurs when the hybridization gap becomes comparable to the disorder strength.
三维拓扑绝缘体的二维表面处于辛的普适类，应该表现出完美的弱反局域化，这反映在正的弱磁场磁阻中。之前拓扑绝缘体薄膜的研究受到高浓度体 n 型掺杂的困扰，使得弱反局域化的定量分析变得困难。在这里，我们测量了体绝缘 Bi2Se3 薄膜的磁阻作为薄膜厚度和栅极调谐载流子密度的函数。对于厚样品，弱反局域化的幅度表明存在两个解耦的（顶部和底部）辛表面。在减小厚度时，我们首先观察到一个交叉到单个辛通道，表明通过层间隧道实现了顶部和底部表面的相干耦合，其次，完全抑制了弱反局域化。第一个交叉由相位相干时间与层间隧穿时间的比值控制，第二个交叉发生在杂化能隙与无序强度相当的时候。
