Spin injection and transport in magnetic-superconducting oxide heterostructures

Advances in thin film deposition techniques, in particular molecular beam epitaxy, have made it possible to produce bilayer heterostructures of high-temperature superconductors and manganite perovskites. The latter exhibit the phenomenon of colossal magnetoresistance (CMR). The half-metallic character of CMR compounds results in their carriers being spin polarized. The geometry of the structures that have been fabricated is such that it is possible to measure the interface conductance-voltage characteristic G(V) as well as the current-voltage characteristic of the superconducting half of the bilayer. Injection of carriers suppresses superconductivity in the latter, with a current gain of order unity. The data exhibit qualitative features of equilibrium theories of spin-polarized transport across an interface between a ferromagnet and an anisotropic superconductor, although a detailed understanding requires generalization of the theory to include out of equilibrium effects.