  The differential resistance of submicron-size ferromagnet/superconductor
interface structures shows asymmetries as a function of the current through the
ferromagnet/superconductor interface. These asymmetries are a consequence of
spin-polarized electron transport from the ferromagnet to the superconductor,
coupled with the Zeeman-splitting of the superconducting quasiparticle density
of states. They are sensitive to the orientation of the magnetization of the
ferromagnet, as the magnetic field required to spin-split the quasiparticle
density of states can be provided by the ferromagnetic element itself.
