Electrically switchable valley polarization and anomalous valley Hall effect in monolayer and bilayer NbS2

Abstract

Achieving electrically controlled valley polarization in ferrovalley materials is critical for their energyefficient valleytronic applications, yet electrical controllability of valley polarization has not been reported in most ferrovalley materials. In this work, the switchable valley polarization in monolayer and bilayer NbS 2 are investigated by first-principles calculations, and it is proposed that the valley polarization in NbS 2 is changeable by a sliding mechanism. It is found that the energy difference of 183 meV between K and K ′ valleys in the valence band can be achieved in monolayer NbS 2 and the relative polarization can be changed by intralayer S atom sliding, which leads to switchable anomalous valley Hall effect. To further decrease the switching barrier, we propose a bilayer NbS 2 scheme which makes use of the A-type interlayer anti-ferromagnetism and the sliding ferroelectricity. It is found that, the change of layer locked half-metallic transport and anomalous valley Hall effect can be achieved in the bilayer NbS 2 by tuning the carrier doping concentration. Moreover, the layer and spin locked valley polarization and valley Hall effect can be well controlled by interlayer sliding. The findings reveal a new mechanism based on atom sliding or layer sliding in electrically controllable valley polarization and anomalous valley Hall effect, which provides a theoretical basis for the design of low-energy valleytronic devices.