Currently, among all known quantum spin Hall (QSH) insulators, square and hexagonal atomic rings are the dominant structural motifs, and QSH insulators composed of pentagonal rings have not yet been reported. Here, we propose a family of large-gap QSH insulators in the SnX2 (X=S, Se, Te) two-dimensional (2D) crystals (121–224 meV). Remarkably, different from all the known QSH insulators, the QSH insulators predicted here are composed entirely of pentagonal rings. Additionally, the considered 2D crystals retain their QSH properties in a quantum well obtained by sandwiching monolayers between two BiOBiS2 sheets, thus providing a viable way for further experimental studies.
- Yandong Ma
- Liangzhi Kou
- Thomas Heine
