Theory of Half Metal/Superconductor Heterostructures

•Juha Kopu1, Matthias Eschrig1, Juan Carlos Cuevas1 und Gerd Schön1,2
2Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76021 Karlsruhe
1Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe

Heterostructures combining superconductors and ferromagnetic materials are promising candidates for applications in the emerging field of spin electronics. In most device proposals, a high degree of polarization of the ferromagnet is desirable. The recently discovered half metals, with one spin band metallic and the other insulating, are ideal materials in this respect. We investigate the Josephson coupling between two singlet superconductors separated by a half-metallic magnet. The mechanism behind the coupling is provided by the rotation of the quasiparticle spin in the superconductor during reflection events at the interface with the half metal. Spin rotation induces triplet correlations in the superconductor which, in the presence of surface spin-flip scattering, result in an indirect Josephson effect between the superconductors. We present a theory appropriate for studying this phenomenon and calculate physical properties for a superconductor/half metal/superconductor heterostructure.