We calculate current, spin current and tunnel magnetoresistance (TMR) for a quantum dot coupled to ferromagnetic leads in the presence of a square wave of bias voltage. Our results are obtained via time-dependent nonequilibrium Green function. Both parallel and antiparallel lead magnetization alignments are considered. The main findings include a wave of spin accumulation and spin current that can change sign as the time evolves, spikes in the TMR signal and a TMR sign change due to an ultrafast switch from forward to reverse current in the emitter lead.
@article{arxiv.0806.4193,
title = {Spin polarized transport driven by square voltage pulses in a quantum dot system},
author = {F. M. Souza and J. A. Gomez},
journal= {arXiv preprint arXiv:0806.4193},
year = {2015}
}