Films based on group IV–V–VI elements for the design of a large-gap quantum spin Hall insulator with tunable Rashba splitting

Rashba spin-orbit coupling (SOC) in topological insulators (TIs) has recently attracted significant interest due to its potential applications in spintronics. However, to date, the coexistence of a giant Rashba SOC and band topology has rarely been investigated in two-dimensional (2D) films. Herein, we applied firstprinciples calculations to design a family of large-gap 2D topological insulators composed of hexagonal Bi and PbX (X = F, Cl, Br, and I) dimers. The nontrivial topology, induced via a p(xy)-p(z) band inversion, was confirmed by the Z(2) index and helical edge states. Note that the Rashba splitting energy in these films reaches 81 meV, which is further tunable over a wide range of strains (- 2-14%). Considering the robustness of the band topology on a h-BN substrate, this study provides a route for designing topological spintronic devices based on 2D films consisting of group IV-V-VI elements.