Charge and spin pumping effects in a single-dot Aharonov-Bohm ring with ferromagnetic leads

The pumping of electrons through a single-dot Aharonov-Bohm ring attached to ferromagnetic leads are investigated theoretically by using the nonequilibrium Green's function method. It is found that the charge and spin pumping effects at zero-bias voltage can be produced by an oscillating electric field applied to the quantum dot. The pumped charge and spin currents through the single-dot ring are analyzed for two cases: (i) the single-dot ring is connected with two ferromagnetic leads and (ii) the single-dot ring is connected with a ferromagnetic and a normal-metal lead. For the former case, a pure spin current can be generated due to the photon-assisted tunneling effects. For the latter case, both the charge and spin current can be pumped in opposite directions. The control of the pumped spin and charge current by using the magnetic flux through the ring is also discussed.