Dumbbell stanane: a large-gap quantum spin hall insulator.

A quantum spin Hall (QSH) effect is quite promising for applications in spintronics and quantum computations, but at present, can only be achieved at ultralow temperatures. The determination of large-gap QSH insulators is critical to increase the operating temperature. By using first-principles calculations, we demonstrate that the stable hydrogenated stanene with a dumbbell-like structure (DB stanane) has large topological nontrivial band gaps of 312 meV (Γ point) and 160 meV for the bulk, characterized by a topological invariant of Z2 = 1 because of s-pxy band inversion. Helical gapless edge states appear in the nanoribbon structures with high Fermi velocity comparable to that of graphene. The nontrivial topological states are robust against the substrate effects. The realization of this material is a feasible solution for the applications of QSH effects at room temperature and can be beneficial in the fabrication of high-speed spintronics devices.