Correlation-Driven Topological Transition in Janus Two-Dimensional Vanadates.

The appearance of intrinsic ferromagnetism in 2D materials opens the possibility of investigating the interplay between magnetism and topology. The magnetic anisotropy energy (MAE) describing the easy axis for magnetization in a particular direction is an important yardstick for nanoscale applications. Here, the first-principles approach is used to investigate the electronic band structures, the strain dependence of MAE in pristine VSi 2 Z 4 (Z = P, As) and its Janus phase VSiGeP 2 As 2 and the evolution of the topology as a function of the Coulomb interaction. In the Janus phase the compound presents a breaking of the mirror symmetry, which is equivalent to having an electric field, and the system can be piezoelectric. It is revealed that all three monolayers exhibit ferromagnetic ground state ordering, which is robust even under biaxial strains. A large value of coupling J is obtained, and this, together with the magnetocrystalline anisotropy, will produce a large critical temperature. We found an out-of-plane (in-plane) magnetization for VSi 2 P 4 (VSi 2 As 4 ), and an in-plane magnetization for VSiGeP 2 As 2 . Furthermore, we observed a correlation-driven topological transition in the Janus VSiGeP 2 As 2 . Our analysis of these emerging pristine and Janus-phased magnetic semiconductors opens prospects for studying the interplay between magnetism and topology in two-dimensional materials.