We investigate the subgap transport properties of a $S$-$F$-$N_{\mathrm{e}}$ structure. Here $S$ ($N_{\mathrm{e}}$) is a superconducting (normal) electrode, and $F$ is either a ferromagnet or a normal wire in the presence of an exchange or a spin-splitting Zeeman field, respectively. By solving the quasiclassical equations we first analyze the behavior of the subgap current, known as the Andreev current, as a function of the field strength for different values of the voltage, temperature, and length of the junction. We show that there is a critical value of the bias voltage $V^{*}$ above which the Andreev current is enhanced by the spin-splitting field. This unexpected behavior can be explained as the competition between two-particle tunneling processes and decoherence mechanisms originating from the temperature, voltage, and exchange field, respectively. We also show that at finite temperature the Andreev current has a peak for values of the exchange field close to the superconducting gap. Finally, we compute the differential conductance and show that its measurement can be used as an accurate way of determining the strength of spin-splitting fields smaller than the superconducting gap.

• Received 16 March 2012

DOI:https://doi.org/10.1103/PhysRevB.86.060509