From classical to quantum spintronics: Theory of coherent spin injection and spin valve phenomena

We present a theory of coherent quantum transport in ferromagnetic/ nonmagnetic/ ferromagnetic heterojunctions. We predict quantum coherence to give rise to a quantum spin valve effect that, unlike its familiar classical analog, occurs even in the absence of a net spin current through the heterostructure. Thus the relationship between spin and charge transport is qualitatively different in the presence of quantum interference than in the (semi-) classical regime. This has important implications for the design of quantum coherent spintronic devices and the interpretation of experiments.