Quantum spin Hall effect in two-dimensional transition-metal chalcogenides MX5 (M = Zr, Hf and X = S, Se, Te)

Based on first-principles calculations, we have found a family of two-dimensional (2D) transition-metal (TM) chalcogenides MX5 (M = Zr, Hf and X = S, Se, Te) can host quantum spin Hall (QSH) effect. The molecular dynamics (MD) simulations indicate that they are all thermal-dynamically stable at room and high temperature. We have investigated MX5’s electronic properties and found their properties are very similar. The single-layer MX5 are all gapless semimetals without consideration of spin–orbit coupling (SOC). With consideration of SOC, they are all insulators with maximum band gap of 0.187 eV. The evolution of Wannier charge centers (WCC) and edge states confirm they are all QSH insulators. The mechanisms for QSH effect in MX5 originate from the special nonsymmorphic space group features. In addition, the QSH state of MX5 survives at a large range of strain as long as the interchain coupling is not strong enough to reverse the band ordering. Monolayer MX5 expand the TI materials based on TM chalcogenides and may open up a new way to fabricate novel low power spintronic devices.