A novel topological crystalline insulator in planar pentacoordinate OsS2 monolayer

Topological crystalline insulators have been confirmed to be topological insulators whose surface states are protected by the crystalline symmetry. A new type of 2D pentagonal rings anisotropic structure OsS2 is confirmed as 2D topological crystalline insulator with gap of 44.3 meV by two pairs of spin filtering edge states and mirror Chern number CM = 2. The dxz and dyz orbitals of Os atom cross linearly between S and Γ points to form a Dirac cone without spin–orbit coupling effect. Carrier mobility of OsS2 is as high as 3.74 × 104cm2 V−1 s- 1for electrons and 3.33 × 104cm2 V−1 s−1 for holes. The OsS2 monolayer is a high-strength 2D material with the minimum Young’s modulus 153.51 N·m−1. Furthermore, OsS2 shows strong optical absorption in the deep ultraviolet region. The OsS2 monolayer is expected to play important applications in fields of nanoelectronics, spintronics and mechanics owing to its TCI and high carrier mobility.