Band structure, evanescent states, and transport in spin tunnel junctions

First-principles based electronic structure calculations provide important insight into spin-dependent transport in tunnelling junctions with magnetic electrodes. They have shown that Bloch electrons are qualitatively different from free electrons in determining the tunnelling probability and magnetoresistance of tunnelling junctions, and that tunnelling wavefunctions within the barrier region are usually different from those modelled by a simple barrier potential. Several factors are important in determining the tunnelling current and magnetoresistance of a tunnelling junction. These include the symmetry of the Bloch wavefunctions, the presence or absence of interface resonance states, the nature of the chemical bond between the electrode atoms and the atoms in the barrier layer, and the complex bands (evanescent states) within the barrier layer.