Single-parameter quantum valley pumping in graphene with topological line defect

We report a theoretical study of single-parameter quantum valley pumping in graphene with a topological line defect via the Keldysh Green's function method. It is found that the valley pumping currents appear only at large scattering angles, with the negative sign for K valley while positive sign for K' valley. The currents following along the direction of the line defect can reach up to 0.1 mA over a large range of Fermi energies and the driving frequencies of an ac-field, which is beneficial for applications. The high currents origin from the asymmetric scattering in the photon-assisted processes and the special characteristics of electronic state distribution in the line defect. In the case of ferromagnetic lead, the two spin currents flow into different leads, respectively.