Multi-level chiral edge states in Janus M2XS2Se2 (M = V, Ti; X = W, Mo) monolayers with high Curie temperature and sizable nontrivial topological gaps

Quantum anomalous Hall (QAH) insulators with dissipation-less chiral edge channels provide the ideal platforms for the exploration of topological materials and low-power spintronic devices. However, the ultralow operation temperature and small nontrivial gap are the bottlenecks for QAH insulators towards future applications. Here, a new family of QAH insulators, that is, the Janus M2XS2Se2 (M = V, Ti; X = W, Mo) monolayers are proposed, which are ferromagnets with large perpendicular magnetic anisotropy (PMA) and high Curie temperature above room-temperature. Moreover, the present M2XS2Se2 monolayers hold sizable nontrivial topological gaps, resulting in the 1st chiral edge state with Chern number C=-1. Unexpectedly, there also exists an occupied 2nd chiral edge state below the Fermi level. Although all M2XS2Se2 monolayers remain the characteristic of PMA by applying the biaxial strain, various topological phase transitions are present. V2WS2Se2 monolayer preserves the QAH state regardless of strain, while the V2MoS2Se2 and Ti2WS2Se2 monolayers transform from QAH states to metallic states under the tensile strains. The present M2XS2Se2 monolayers show the competitive advantages among the reported materials for the development of topological electronic devices.