Correlation-driven topological phase transition in 2D valleytronic materials: a mini-review

Electronic correlation combined with spin-orbit coupling (SOC) may have a significant impact on the physical properties of two-dimensional (2D) transition metal magnetic compounds. Moreover, magnetic anisotropy (MA) is very important in determining magnetic, ferrovalley (FV) and topological properties of these 2D systems. Based on a density-functional theory (DFT) + U approach, it is found that the electronic correlation can induce topological phase transition in some special 2D valleytronic materials (for example FeCl 2 and VSi 2 P 4 ) with out-of-plane MA, and a novel valley-polarized quantum anomalous Hall insulator (VQAHI) and half-valley-metal (HVM) can be produced. These topological phase transitions are connected with a sign-reversible Berry curvature and band inversion between d xy /d x 2 − y 2 and d z 2 orbitals. However, for in-plane MA, the FV and nontrivial topological properties will be suppressed. For a given material, the correlation strength is fixed, but these novel electronic states and topological phase transitions can still be exhibited by strain in practice. The mini-review sheds light on the possible role of correlation effects in some special 2D valleytronic materials. The ferrovalley semiconductors (FVS) to half-valley-metal (HVM) to valley-polarized quantum anomalous Hall insulator (VQAHI) to HVM to FVS transitions can be driven by increasing electron correlation U in some special 2D valleytronic materials.