Quantum spin Hall states in MX2 (M = Ru, Os; X = As, Sb) monolayers.

The quantum spin Hall (QSH) effect has attracted extensive research interest due to its great promise in topological quantum computing and novel low-energy electronic devices. Here, using first-principles calculations, we find that MX2 (M = Ru and Os; X = As and Sb) monolayers are 2D topological insulators (TIs). The spin-orbit coupling (SOC) band gaps for RuAs2, RuSb2, OsAs2, and OsSb2 monolayers are predicted to be 80, 131, 118, and 221 meV, respectively. Additionally, the nontrivial topological states are further confirmed by calculating the topological invariant and the appearance of gapless edge states. More interestingly, for RuSb2 and OsSb2 monolayers, the position of node points in energy can be effectively tuned by applying in-plane strain. Our results consistently indicate that all MX2 monolayers can serve as an effective platform for achieving the room-temperature QSH effect.