Photon-assisted spin transport in a two-dimensional electron gas

We study spin-dependent transport in a two-dimensional electron gas subjected to an external steplike potential V(x) and irradiated by an electromagnetic field (EF). In the absence of EF, the electronic spectrum splits into spin subbands originating from the "Rashba" spin-orbit coupling. We show that the resonant interaction of propagating electrons with the component EF parallel to the barrier induces a nonequilibrium dynamic gap (2 Delta(R)) between the spin subbands. Existence of this gap results in coherent spin-flip processes that lead to a spin-polarized current and a large magnetoresistance, i.e., the spin-valve effect. These effects may be used for controlling spin transport in semiconducting nanostructures, e.g., spin transistors, spin-blockade devices, etc., by variation of the intensity S and frequency omega of the external radiation.