Spin-active scattering matrices for interfaces between superconductors and half metals

Recently a non-vanishing supercurrent has been observed in a Josephson junction that contains an extended region of half-metallic CrO2 between two singlet superconducting electrodes. A theory to explain this phenomenon has been established in Refs. [2,3] that is formulated in terms of spin-active interface scattering matrices. Spin mixing and breaking of spin-rotation symmetry around the magnetization axis of the half metal are necessary ingredients for creation of equal spin triplet pairing amplitudes that can penetrate the half metal over a long range. Here, we present a microscopic model for a scattering matrix that exhibits such characteristics. We show that disorder of local magnetic moments at the interface between a superconductor and a ferromagnet with biaxial anisotropy in the interface region leads to the observed current conversion between singlet and equal spin triplet supercurrents. We discuss our results by comparing with the experimental findings of biaxial anisotropy and triplet supercurrents in the half metal CrO2. (orig.)