Spin Transport in a Rashba Ring-Quantum Dot System Pumped by Microwave Fields

We report a theoretical study on producing electrically spin-polarized current in the Rash baring with parallel double dots embedded, which are subject to two time-dependent microwave fields. By means of the Keldysh Green's function method, we present an analytic result of the pumped current at a diabatic limit and demonstrate that the interplay between the quantum pumping effect and spin-dependent quantum interference can lead to an arbitrarily controllable spin-polarized current in the device. The magnitude and direction of the charge and spin current can be effectively modulated by system parameters such as the pumping phase difference, Rashba precession phase, and the dynamic phase difference of electron traveling in two arms of ring; moreover, the spin-polarization degree of the charge current can also be tuned in the range [-infinity,+infinity]. Our findings may shed light on the all-electric way to produce the controllable spin-polarized charge current in the field of spintronics.