Functionalized bismuth films: Giant gap quantum spin Hall and valley-polarized quantum anomalous Hall states

The search for new large band gap quantum spin Hall (QSH) and quantum anomalous Hall (QAH) insulators is critical for their realistic applications at room temperature. Here we predict, based on first-principles calculations, that the band gap of QSH and QAH states can be as large as 1.01 and 0.35 eV in an H-decorated Bi(111) film. The origin of this giant band gap lies in both the large spin-orbit interaction of Bi and the H-mediated exceptional electronic and structural properties. Moreover, we find that the QAH state also possesses the properties of a quantum valley Hall state, thus intrinsically realizing the so-called valley-polarized QAH effect. We further investigate the possibility of large gap QSH and QAH states in an H-decorated Bi((1) over bar 10) film and X-decorated (X = F, Cl, Br, and I) Bi(111) films.