Quantum spin Hall state in cyanided dumbbell stanene

Searching for two-dimensional (2D) quantum spin Hall (QSH) insulators with a large band gap, in which the Quantum spin Hall effect (QSHE) can be observed at high temperature, is an important goal for condensed matter physics researchers. Based on first principles calculations, we predict that the band gap of dumbbell stanene can be enhanced to 52 meV with cyano group decoration (DB-SnCN), which can be further tuned to be 322 meV by applying lattice strains. The band topology is identified by Z(2) topological invariance together with helical edge states, and the mechanism can be understood with p(x)-p(y) band inversion at the Gamma point induced by spin-orbit coupling (SOC). These findings provide bright and significant guidance for future fabrication and realistic applications of spintronics.