Topological phase transition due to strain-controlled evolution of the inverted bands in 1T′-MX2
AbstractFirst-principles calculations have been performed to study the evolution of the inverted bands and the topological phase diagrams of monoclinic transition-metal dichalcogenide monolayers (1T′-MX2 with M=Mo, W and X=S, Se, Te) under strain. We find that the band topology undergoes a nontrivial to trivial transition in compressed systems due to the strain-sensitive inverted p-orbital and d-orbital bands, which exhibit an anisotropic evolution behavior with respect to the strain orientation. In MTe2, the normally ordered py and d bands at the X point are inverted mainly by compressive strain along the y direction (εy), which, together with the unchanged inverted bands at the Γ point, turns the topology trivial. In MS2 and MSe2, the inverted px and d bands at Γ become normally ordered under a large compressive strain along the x direction (εx). MTe2 acquires a much smaller critical strain for the topological phase transition (TPT) than S- and Se-based systems due to strain-sensitive head-to-head bonding between the py orbitals. Particularly, the critical compressive εy can be further reduced by applying tensile εx for MTe2. Our results provide a concrete mechanism behind the nontrivial band topology in 1T′-MX2 and a guide for applying strain to control the TPT.