Sudden gap closure across the topological phase transition in Bi2-xInxSe3

Abstract

The phase transition from a topological insulator to a trivial band insulator is studied using angle-resolved photoemission spectroscopy on Bi2-xInxSe3 single crystals. We first report the complete evolution of the bulk band structures throughout the transition. The robust surface state and the bulk-gap size (∼0.50eV) show no significant change upon doping for x=0.05, 0.10, and 0.175. At x≥0.225, the surface state completely disappears and the bulk-gap size increases, suggesting a sudden gap closure and topological phase transition around x∼0.175-0.225. We discuss the underlying mechanism of the phase transition, proposing that it is governed by the combined effect of spin-orbit coupling and interactions upon band hybridization. Our study provides a venue to investigate the mechanism of the topological phase transition induced by nonmagnetic impurities.