Quantum Valley Hall Effect for Bosons

Abstract

We predict the emergence and quantization of the valley Hall current of indirect excitons residing in a noncentrosymmetric two-dimensional material. This current appears due to the anomalous group velocity of exciton center-of-mass motion with an account of the Berry phase of individual electrons and holes in the exciton within a given valley and in the presence of the quasi-condensate. In equilibrium, the net exciton flux vanishes. However, under the action of an external electromagnetic field, the excitons pushed out from the ground state contribute to stationary nonequilibrium valley Hall current, which exhibits a quantized behavior as a function of electromagnetic field frequency.