Pure valley-polarized current in graphene junction induced by circularly polarized light and carrier mass

In this work, we presented a workable scheme to induce valley polarized current in a graphene junction with circularly polarized light and carrier mass. A non-linear effect of the circularly polarized light opens a gap in the Dirac cone. The mass term corresponding to a symmetry-breaking perturbation admits a band gap. The result shows that a valley-dependent energy gap can be opened in the presence of both circularly polarized light and carrier mass. We found that pure valley-polarized current is achieved in the valley-dependent energy gap. However, only one of the two modulations is present, no valley polarization can be generated. So the combination of the two modulations provides a new way to producing the pure valley current in the graphene system.