Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions

摘要

Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagneticjunctions is studied theoretically within the Landauer framework of ballistictransport. We show that quantum coherence can have unexpected implications forspin injection and that some intuitive spintronic concepts which are founded insemi-classical physics no longer apply: A quantum spin-valve (QSV) effectoccurs even in the absence of a net spin polarized current flowing through thedevice, unlike in the classical regime. The converse effect also arises, i.e. azero spin-valve signal for a non-vanishing spin-current. We introduce newcriteria useful for analyzing quantum and classical spin transport phenomenaand the relationships between them. The effects on QSV behavior ofspin-dependent electron transmission at the interfaces, interface Schottkybarriers, Rashba spin-orbit coupling and temperature, are systematicallyinvestigated. While the signature of the QSV is found to be sensitive totemperature, interestingly, that of its converse is not. We argue that the QSVphenomenon can have important implications for the interpretation ofspin-injection in quantum spintronic experiments with spin-valve geometries.