Sudden gap closure across the topological phase transition inBi2−xInxSe3

Abstract

The phase transition from a topological insulator to a trivial band insulator is studied using angle-resolved photoemission spectroscopy on ${\mathrm{Bi}}_{2\ensuremath{-}x}{\mathrm{In}}_{x}{\mathrm{Se}}_{3}$ 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 ($\ensuremath{\sim}0.50\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$) show no significant change upon doping for $x=0.05$, 0.10, and 0.175. At $x\phantom{\rule{0.16em}{0ex}}\ensuremath{\ge}0.225$, the surface state completely disappears and the bulk-gap size increases, suggesting a sudden gap closure and topological phase transition around $x\ensuremath{\sim}0.175--0.225$. 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.