Quantum spin Hall effect and tunable topological states in M2O3 (M = Nb, Ta) bilayers

Abstract

As a platform for realizing the quantum spin Hall (QSH) effect, two-dimensional (2D) topological insulators show great promise for applications in low-power electronic devices. Here, we explore the topological properties of 2D M2O3 (M = Nb, Ta) by using first-principles calculations. We identify the Nb2O3 monolayer as a robust Chern insulator with chiral edge states, while Ta2O3 monolayer is a semiconductor with a moderate band gap. Interestingly, both Nb2O3 and Ta2O3 bilayers are found to be QSH insulators with sizable bulk band gaps of 85 meV and 212 meV, respectively, as evidenced by the analysis of topological invariants and edge state calculations. Remarkably, a topological phase transition from a topological insulator to a Dirac semimetal occurs in the Nb2O3 bilayer under compressive strain. Our studies not only uncover novel topological physics characteristics, but also offer a unique quantum material platform for exploring low-power electronic devices.