Coherent effect in normal-metal/ferromagnetic superconductor/normal-metal double tunnel junctions

Taking simultaneously into account the electron-injected current from one normal-metal (N) electrode and the hole-injected current from the other N electrode, we present a theory of the coherent quantum transport in N/ferromagnetic superconductor (FS)/N double tunnel junctions, and derive a general formula for the differential conductance. It is shown that the conductance spectrum exhibits an oscillatory behavior with the bias voltage, and the oscillation amplitude is reduced with both increasing temperature and increasing exchange energy in the FS. The exchange energy also leads to a Zeeman splitting of the conductance peaks and in the tunnel limit to the formation of a series of quasiparticle bound states in the FS.