Subgap conductance in ferromagnet-superconductor mesoscopic structures

We study the subgap conductance of a ferromagnetic mesoscopic region attach ed to a ferromagnetic and a superconducting electrode by means of tunnel ju nctions. In the absence of the exchange field, the ratio r = gamma/epsilon( T) Of the two-tunnel junction resistances determines the behavior of the su bgap conductance, which possesses a zero-bias peak for r much greater than 1 and for r much less than 1 a peak at finite voltage. We show that the inc lusion of the exchange field leads to a peak splitting for r much less than 1, while it shifts the zero-bias anomaly to finite voltages for r much gre ater than 1. [S0163-1829(99)01219-9].