Large-Gap Two-Dimensional Topological Insulator State in Oxygen Functionalized Mxene-Type Chromium Group Silicides

Abstract

Exploring two-dimensional (2D) materials with particular properties is essential for the development of nano-scale electronics devices. Here, we studied a new class of 2D MXene-type chromium group silicide (M2Si, M = Cr, Mo, W), based on first-principles calculations. The Cr2Si monolayer is an AFM metal with large local spin moment on the Cr atoms. The Mo2Si and W2Si monolayers are nonmagnetic metals but their lattices are dynamically unstable. Interestingly, the Mo2Si and W2Si monolayers can be stabilized by oxygen functionalization, resulting in giant topological insulator (TI) gap up to 199 meV. Analysis of the electronic structures reveals that the strong spin-orbit coupling effect in the W-5d orbital is responsible for the large TI gap. Furthermore, the TI gap is robust against moderate biaxial strain, which could benefit the realization of the quantum spin Hall effect at room temperature in experiment.

Keywords: Transition metal silicides, 2D Mxene, Antiferromagnetism, Topological Insulator