Topological phase transition with tunable orbital Hall effect in two-dimensional ferromagnet SVSiN2

We theoretically show the switching between topologically nontrivial phases characterized by different bulk-boundary correspondences and, in particular, establish the intrinsic coupling between band topology and orbital Hall effect in two-dimensional (2D) ferromagnets. We further emphasize that the variation of orbital angular momentum induced by topological phase transitions accompanied by band inversion plays a crucial role in modulating the magnitude of the orbital Hall conductivity. Taking the hexagonal Janus SVSiN2 monolayer as a representative material candidate, we validate the feasibility of our proposal. The material hosts the 2D second-order topological insulator with intrinsic ferromagnetism, and strain-induced valley modulation drives successive topological phase transitions from second-order topological insulators to Chern insulator and, finally, to normal insulator. The topologically nontrivial natures in SVSiN2 are confirmed through the analysis of corner states, edge states, and Chern numbers. Notably, the topological phase transitions give rise to a switchable orbital Hall effect, highlighting their critical role in modulating orbital transport. These findings underscore the profound connection between nontrivial topology and the orbital Hall effect, opening promising avenues for future advances in topological spintronics and orbitronics.