  Based on the Keldysh Green's function method, we report an unconventional
two-parameter quantum pumping in graphene with a line defect. It is found that
different from the conventional sinusoidal relation, the pumped current in this
device is cosinusoid dependence on the phase difference between the two pumping
potentials, which adopts its positive/nagative maximum value at while tends to
zero at . This phenomenon is related to the peculiar valley tunneling
characteristics across the line defects and the exchange of valley indices on
both sides of the line defect. Moreover, the pumped currents from the two
valleys will flow in opposite directions along the line defect, indicating that
the controllable valley current can be pumped out in the line defect without
the application of strain field in graphene.
