  Two-dimensional quantum spin Hall (QSH) insulators with reasonably wide band
gaps are imperative for the development of various innovative technologies.
Through systematic density functional calculations and tight-binding
simulations, we found that stanene on {\alpha}-alumina surface may possess a
sizeable topologically nontrivial band gap (~0.25 eV) at the {\Gamma} point.
Furthermore, stanene is atomically bonded to but electronically decoupled from
the substrate, providing high structural stability and isolated QSH states to a
large extent. The underlying physical mechanism is rather general, and this
finding may lead to the opening of a new vista for the exploration of QSH
insulators for room temperature device applications.
