Strain-driven topological phase transition between anomalous valley Hall and quantum anomalous Hall states in hexagonal ferromagnets

Abstract

The anomalous valley Hall (AVH) effect, characterized by a polarized valley degree of freedom, provides a route toward a valley-dependent quantum anomalous Hall (QAH) state. Yet, realizing both in one material remains challenging due to their distinct Chern number requirements. We propose a general strategy for a strain-tunable topological transition in hexagonal ferromagnets. In the inversion-broken system, spin–orbit coupling yields valley polarization with valley-contrasted Chern numbers (C = ±1/2). Strain closes and reopens the gap at one valley, driving band inversion that switches the total Chern number to C = −1, transforming the system into a QAH phase with a single chiral edge channel. This strain-driven transition is demonstrated in monolayers of FeXY (X ≠ Y; Cl, Br, I), ScBr2, and VSi2P4. These results highlight the key role of strain engineering in controlling valley topology and provide a viable route toward valleytronic and topotronic applications.