Photon-mediated spin-polarized current in a quantum dot under thermal bias

Spin-polarized current generated by thermal bias across a system composed of a quantum dot (QD) connected to metallic leads is studied in the presence of magnetic and photon fields. The current of a certain spin orientation vanishes when the dot level is aligned to the lead's chemical potential, resulting in a 100% spin-polarized current. The spin-resolved current also changes its sign at the two sides of the zero points. By tuning the system's parameters, spin-up and spin-down currents with equal strength may flow in opposite directions, which induces a pure spin current without the accompany of charge current. With the help of the thermal bias, both the strength and the direction of the spin-polarized current can be manipulated by tuning either the frequency or the intensity of the photon field, which is beyond the reach of the usual electric bias voltage.