Mesoscopic spin-flip transport through a quantum dot systemresponded by ac magnetic fields

We investigate mesoscopic spin transport through a quantum dot(QD) responded by a rotating and an oscillating magneticfields. The rotating magnetic field rotates with the angularfrequency 0 around the z-axis with the tilt angle, while the time-oscillating magnetic field is located inthe z-axis with the angular frequency . The spin flip iscaused by the rotating magnetic field, and it is the major sourceof spin current. The Zeeman effect is contributed by the two fieldcomponents, and it is important as the magnetic fields are strong.The oscillating magnetic field takes significant role due to thespin-photon pumping effect, and the spin current can be generatedby it even as 00 for the tilt angle0. The peak and valley structure appears with respectto the frequency of oscillating field. The generation ofspin current is companying with charge current. Spin currentdisplays quite different appearance between the cases in theabsence of source-drain bias (eV=0) and in the presence ofsource-drain bias (eV0). The symmetric spin currentdisappears to form asymmetric spin current with a negative valleyand a positive plateau. The charge current is mainly determined bythe source-drain bias, photon absorption, and spin-flip effect.This system can be employed as an ac charge-spin currentgenerator, or ac charge-spin field effect transistor.