Electric control of Chern number in valley-polarized quantum anomalous Hall insulators†

Abstract

The valley-polarized quantum anomalous Hall effect has attracted considerable interest in the condensed matter field due to the topologically protected edge states with a unique valley index. Here, using first-principles calculations, we demonstrate that the valley-polarized quantum anomalous Hall effect with a tunable Chern number can be realized in a Cr₂COH monolayer through external electric fields. Our results show that the Cr₂COH monolayer is a ferrovalley system with spontaneous valley polarization. Valley polarization originates from broken spatial inversion and time-reversal symmetries, giving rise to the anomalous valley Hall effect and the valley-polarized quantum anomalous Hall effect. Remarkably, an out-of-plane external electric field induces valley-contrasted Stark shifts, resulting in the energy gap closing and reopening in these valleys, thereby facilitating the manipulation of the Chern number from C = −1 to C = −3 in valley-polarized QAH insulators. Our findings provide a guide for designing quantum devices based on the valley-polarized quantum anomalous Hall effect.