Alloying-induced topological transition in 2D transition-metal dichalcogenide semiconductors

Research on two-dimensional (2D) topological insulators (TIs) is obstructed due to the lack of feasible approaches to growing 2D TIs in experiments. Through systematic first-principles calculations and tight-binding simulations, we propose that alloying Os in 2D MoX2 (X = S, Se, Te) monolayers is an effective approach to inducing semiconductor-to-TI transitions, with sizable nontrivial gaps of 25-37 meV. Analysis of the electronic structures reveals that the topological property mainly originates from the 5d orbitals of the Os atom. Furthermore, the TI gaps can be modulated by external biaxial strain.