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