Barrier-induced enhancement of Andreev reflection for minority-spin quasiparticles in ferromagnetic metal/insulator/superconductor ballistic junctions

The Andreev reflection probability in ferromagnetic metal/superconductor ba llistic junctions depends on the spin orientation of the incident quasipart icle when a barrier of low or moderate strength is present at the interface . In contrast to the common conception that a barrier always reduces Andree v reflection probability, this probability is enhanced for quasiparticles i n the minority spin band only, due to a reduction in the phase shift of the wave function. Because of the Andreev reflection probability enhancement, which is predicted to be below the superconducting gap near the gap edge, t he total subgap conductance exhibits characteristic weak but measurable fea tures (maxima).