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 C_M = 2. The d_xz and d_yz 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^{- 1}for 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.