Realizing high-performance quantum anomalous Hall insulators by surface halogenation

Although numerous methods have been proposed to realize the quantum anomalous Hall (QAH) effect, the high-performance QAH effect is yet limited. In this study, the surface halogenation strategy is applied to trigger the QAH states in a series of group-VIB transition metal dichalcogenide monolayers. All MoS₂Cl₂, MoSe₂Cl₂, and MoTe₂Cl₂ monolayers present a high Chern number $C=-2$, and their nontrivial topological gaps are 23.5, 55.9, and 83.6 meV, respectively. Both the MoS₂Cl₂ and MoSe₂Cl₂ possess in-plane magnetic anisotropy, showing a Berezinskii-Kosterlitz-Thouless transition temperature of 432 and 450 K. The MoTe₂Cl₂ exhibits an out-of-plane magnetic anisotropy and Curie temperature up to 521 K. The ferromagnetism of MoX₂Cl₂ monolayers originates from the modulation of valence electron filling via surface halogenation. The realization of QAH states by surface halogenation is also demonstrated in WX₂Cl₂, WX₂Br₂, and MoX₂Br₂ monolayers. This work offers insights for designing novel QAH insulators, facilitating the development of topological electronic devices.