Spin-polarized transport through a two-level quantum dot driven by ac fields

We study the spin-polarized current and shot noise spectra in a two-level quantum dot driven by ac fields, where the dot is connected to two ferromagnetic leads with parallel alignment. When the spin-resolved interlevel pump is applied, it is demonstrated that a pure spin current can be generated at zero bias voltage. We separately discuss the transport properties in two tunneling regimes, double levels of the quantum dot under the transport windows and dynamical channel blockade regimes. It is found that Fano factor relies sensitively not only on the pump style but also on the corresponding strength. When both levels lie in the transport window, the Fano factor is independent on the charge pump but decreases with the spin pump strength. In the channel blockade case, different combinations of sub- and super-Poissonian Fano factors are shown in various regimes by tuning the pump strength and spin polarization. The results indicate that the shot noise can be used to detect the inner interactions and physical properties in the present device. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552308]