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

Abstract

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 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 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.