Built-in electric field and strain tunable valley-related multiple topological phase transitions in VSiX N4(X= C, Si, Ge, Sn, Pb) monolayers

Valley-related multiple topological phase transitions have attracted significant attention because they provide significant opportunities for fundamental research and practical applications. Unfortunately, however, there is no real material as of yet that can realize valley-related multiple topological phase transitions. Here, through first-principles calculations and model analysis, we investigate the structural, magnetic, electronic, and topological properties of VSiXN4(X=C,Si,Ge,Sn,Pb) monolayers. VSiXN4 monolayers are stable and intrinsically ferrovalley materials. Intriguingly, we found that built-in electric field and strain can induce valley-related multiple topological phase transitions in materials from valley semiconductor to valley half-semimetal, to valley quantum anomalous Hall insulator, to valley half-semimetal, and to valley semiconductor (or to valley metal). The nature of the topological phase transition is the built-in electric field and strain-induced band inversion between the dxy/dx2-y2 and dz2 orbitals at K and K′ valleys. Our findings not only reveal the mechanism of multiple topological phase transitions, but they also provide an ideal platform for the multifield manipulating the spin, valley, and topological physics. This will lead to alternative perspectives for spintronic, valleytronic, and topological nanoelectronic applications based on these materials.