Spin-dependent transport in ferromagnet/semiconductor/ferromagnet junctions: a fully relativistic approach

We present a fully relativistic generalization of the Landauer-Buttiker formalism that has been implemented within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker Green function method. This approach, going beyond the two-current model, supplies a more general description of the electronic transport. It is shown that the relativistic conductance can be split in terms of individual spin-diagonal and spin-off-diagonal (spin-flip) components, which allows a detailed analysis of the influence of spin-orbit-coupling-induced spin-flip processes on the spin-dependent transport. We apply our method to calculate the ballistic conductance in Fe/GaAs/Fe magnetic tunnel junctions. We find that, by removing the spin selection rules, the spin-orbit coupling strongly influences the conductance, not only qualitatively but also quantitatively, especially in the anti-parallel alignment of the magnetization in the two Fe leads.