Time-dependent spin-polarized transport through a resonant tunneling structure with multiterminals

The spin-dependent transport of electrons tunneling through a resonant tunneling structure with ferromagnetic multiterminals under dc and ac fields is explored by means of the nonequilibrium Green function technique. A general formulation for the time-dependent current and the time-averaged current is established. Its application to systems with two and three terminals in noncollinear configurations of the magnetizations under dc and ac biases are investigated. The present three-terminal which is coined as a spin transistor with source, device, is different from that discussed in the literature. A current-amplification effect is found. In addition, time-dependent spin transport for the two-terminal device is studied. It is found that the photonic sidebands provide new channels for electrons tunneling through the barriers, and give rise to new resonances of the tunneling magnetoresistance, which is called photon-assisted spin-dependent tunneling. Some relevant issues are discussed.