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 ideal platforms for the exploration of topological materials and low-power spintronic devices. However, the ultralow operation temperature and small nontrivial gaps are the bottlenecks for QAH insulators towards future applications. Here, a new family of QAH insulators, that is, Janus M₂XS₂Se₂ (M = V, Ti; X = W, Mo) monolayers, are proposed to be 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 1^st chiral edge state with Chern number C = −1. Unexpectedly, there also exists an occupied 2^nd chiral edge state below the Fermi level. Although all M₂XS₂Se₂ monolayers retain their PMA characteristics on application of biaxial strain, various topological phase transitions are present. The V₂WS₂Se₂ monolayer preserves the QAH state regardless of strain, while the V₂MoS₂Se₂ and Ti₂WS₂Se₂ monolayers transform from QAH states to metallic states under tensile strains. The present M₂XS₂Se₂ monolayers show competitive advantages among the reported materials for the development of topological electronic devices.