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

摘要

We investigate mesoscopic spin transport through a quantum dot (QD) responded by a rotating and an oscillating magnetic fields. The rotating magnetic field rotates with the angular frequency omega(0) around the z-axis with the tilt angle theta, while the time-oscillating magnetic field is located in the z-axis with the angular frequency omega. The spin flip is caused by the rotating magnetic field, and it is the major source of spin current. The Zeeman effect is contributed by the two field components, and it is important as the magnetic fields are strong. The oscillating magnetic field takes significant role due to the spin-photon pumping effect, and the spin current can be generated by it even as omega(0) --> 0 for the tilt angle theta not equal 0. The peak and valley structure appears with respect to the frequency omega of oscillating field. The generation of spin current is companying with charge current. Spin current displays quite different appearance between the cases in the absence of source-drain bias (eV = 0) and in the presence of source-drain bias ( eV not equal 0). The symmetric spin current disappears to form asymmetric spin current with a negative valley and a positive plateau. The charge current is mainly determined by the source-drain bias, photon absorption, and spin-flip effect. This system can be employed as an ac charge-spin current generator, or ac charge-spin field effect transistor.