Exotic quantum spin Hall effect and anisotropic spin splitting in carbon based TMC6 (TMÂ =Â Mo, W) kagome monolayers

Two dimensional topological insulators with high feasibility and room-temperature band gaps are desirable at present. Here, kagome monolayers TMC6 (TM = Mo, W) are systematically investigated by density functional theory and molecular dynamics simulations. TMC6 lattice with one TM layer sandwiched between two trigonal carbon layers is proved to be stable. We identify that band inversion occurs in TMC6 with opened gaps up to 226 meV, making the system suitable for room temperature applications. By analyzing orbital resolved band structures and partial charge densities, we determine that the band inversion is mainly contributed by TM-d orbitals after introducing spin orbit coupling. The nontrivial topological feature is confirmed by direct calculation of Z2 invariant (Z2 = 1) indicating that TMC6 is quantum spin Hall (QSH) insulator. Distinct from previous QSH insulators, there is spin splitting along Γ→K direction (perpendicular to the mirror plane), while there is no splitting along Γ→M direction (parallel to the mirror plane). Further investigation unravels that the anisotropic spin splitting could be attributed to the in-plane structural inversion asymmetry. TMC6 kagome monolayers with nontrivial topology and anisotropic spin splitting could open up a way for new generation spintronic and electronic devices.