New quantum spin Hall insulator in two-dimensional MoS2 with periodically distributed pores

Abstract

MoS₂, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS₂ (g-MoS₂), consisting of MoS₂ squares and hexagons. g-MoS₂ has a nontrivial gap as large as 109 meV, comparable with previously reported 1T′-MoS₂ (80 meV) and so-MoS₂ (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS₂ originates from the pure d–d band inversion, different from the conventional band inversion between s–p, p–p or d–p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications.