Tunneling resonances and Andreev reflection in transport of electrons through a ferromagnetic metal/quantum dot/superconductor system

We calculate the transport properties of a ferromagnetic metal/quantum dot/superconductor system by the use of the equivalent single-particle multichannel network that takes into account the interaction in the dot and the pairing potential on the superconducting side. The transport properties are qualitatively different from the nonmagnetic case due to the modification of the Andreev reflection by the exchange field in the ferromagnet. It is found that at finite temperatures the conductance versus the gate voltage exhibits a series of peaks due to the Andreev reflection, depending on the resonances controlled by the charging energy and level spacing of the dot, as well as by the exchange field of the ferromagnet. The zero-bias conductance of the system can either be enhanced or suppressed by the exchange field, depending on the matching condition of the Fermi velocity which is related to the electron occupation in this structure.