Pseudo lattice-breathing driven valley switching in 2D ferromagnetic lattices

Valley manipulation has garnered significant attention due to its exceptionally rich physics and potential device applications. Although the current research predominantly relies on magnetic fields to control the valley degree of freedom, alternative strategies of switching the valley index remain largely unexplored. Here, using symmetry analysis and a low-energy effective model, we propose a novel mechanism for valley index reversal in a two-dimensional (2D) ferromagnetic lattice via pseudo lattice-breathing. This mechanism arises from vertical sliding-modulated exchange of sublattice potentials acting on the trigons formed by magnetic atoms, resulting in a pseudo lattice-breathing mode. As such trigons are intimately linked to valley properties, the pseudo lattice-breathing effectively switches the valley state. The general design principles and material constraints for realizing this effect are also established. Through first-principles calculations, we demonstrate this mechanism in the EuGe₂ monolayer. Our work opens a new avenue for valleytronics in 2D systems.