Pumped charge and spin current in a quantum dot molecule

The effects of an ac electric field on the quantum transport behaviors in a parallel-coupled double quantum dot system are investigated theoretically. A dc charge current can be pumped at zero bias due to photon-assisted tunneling effects. The sign, magnitude and position of the pumped current peaks can be well controlled and manipulated by simply varying the gate voltage, the amplitude and frequency of the ac field. Furthermore, the possibility of electrically pumping a pure spin current in the presence of spin-orbit interaction is discussed.