Predicting quantum spin hall effect in graphene/GaSb and normal strain-controlled band structures

Graphene (Gr) has been demonstrated to be a two dimensional (2D) topological insulator (TI) with an opened spin-orbit coupling (SOC) energy gap at Dirac point. The extremely small energy gap, however, makes the predicted quantum spin Hall (QSH) effect difficult to be observed at room temperature. In present work, we propose an effective way to tune the energy gap of Gr by combining with GaSb. The intrinsic bulk gap of Gr reaches up to 125 meV and 116 meV in Gr/(Ga)Sb and Gr/Ga(Sb), respectively, which makes it available in practical applications. Moreover, the energy gap of Gr can be opened and increased to 147 meV in GaSb/Gr/GaSb by hydrogen passivation. The inverted band ordering and gapless edge states further demonstrate that our considered heterostructures possess QSH effect. Normal strain engineering leads to effective control and substantial enhancement of their energy gap and band inversion. Hexagonal boron nitride (h-BN) is also verified to be a suitable substrate to supporting films without destroying their QSH effect. Our results provide feasible platform to design Gr-based spintronics devices.