Gate voltage induced topological phase transition in hexagonal boron-nitride bilayers

Abstract

Single or few-layer hexagonal boron nitride sheets usually have very large band gaps, which greatly hinders their applications in electronic circuits. In this letter, we propose a way to significantly reduce the band gap of hexagonal boron-nitride bilayer (BNBL) by applying an interlayer bias voltage. In the presence of the intrinsic and Rashba spin-orbit couplings, we demonstrate whether gated BNBL is topologically nontrivial depends strongly on its stacking type. For AA-stacking BNBL with inversion symmetry, the strong topological insulator phase is obtained, and phase boundaries are analytically given. We also observe a re-entrant phase behavior from a normal insulator to a topological insulator then to a normal insulator, which is switched by the gate voltage. For AB-stacking BNBL, it is always topologically trivial but exhibits an unusual quantum Hall phase with four degenerate low-energy states localized at a single edge. These findings provide potential applications of BNBLs in electronics and spintronics.