Robustness of the quantum spin Hall insulator phase in monolayer 1T′ transition metal dichalcogenides

The metastable 1T′ structural phase of monolayer transition metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) has been predicted to host the quantum spin Hall (QSH) phase. We report a first-principles investigation of the robustness of the QSH phase with respect to the variation of the lattice constants. The band inversion responsible for the emergence of the QSH phase was found to persist in a broad range of strains for most of the materials. However, the magnitude of the electronic band gap is sensitive to the changes of the lattice constants, which points at possibly inconsistent band gaps calculated using different computational methodologies. Our results point out that the band gaps of the topologically nontrivial monolayer 1T′ transition metal dichalcogenides can be experimentally controlled by moderate strains.