Strain-driven valley-dependent Berry phase effects and topological transitions in Janus SVGeN2 monolayer

The manipulation of valley-dependent properties in two-dimensional (2D) materials is intriguing for developing valleytronics. Using first-principles calculations, we explore valley-dependent properties of Janus SVGeN2 monolayer and reveal large and tunable valley polarization by tensile strain. The SVGeN2 monolayer possesses excellent stability. Furthermore, strain-driven topological magneto-valley phase transitions are predicted for this monolayer, leading to the valley quantum anomalous Hall (VQAH) phenomenon. The VQAH state, which is featured by the coexistence of complete valley polarization and topological phase, is confirmed by sign reversal of Berry curvature and the nontrivial band topology. The calculated magnetic anisotropy energy indicates that the Janus SVGeN2 monolayer possesses a ferromagnetic ground state and in-plane magnetization. Our investigation provides some physical insights into the strain-driven topological phase transition and manipulation of valley-dependent properties to realize giant valley polarization in the Janus 2D magnet.