Current–voltage characteristics and conductance spectra in s-wave or d-wave superconductor/ferromagnet/superconductor heterojunctions: role of Andreev reflection

In recent years, the investigation of transport properties of hybrid structures consisting of two superconductors connected by a ferromagnet has been the subject of many studies. Their dynamic properties are closely related to the Andreev scattering and spin polarization in ferromagnet barrier. This kind of junction offer the possibility to study interplay between the phase coherent propagation of Andreev pairs and various decoherence mechanisms. We review a quantitative theory developed in the last decade for describing quasiparticle transport properties in superconductor/ferromagnet (F)/superconductor junctions where superconducting electrodes could have s-wave (SFS junction) or d-wave (DFD junction) symmetry. In the relaxation-time approximation utilizing the time-dependent Bogoliubov–de Gennes equations the current–voltage characteristic and conductance are calculated. The obtained results provides possibility to experimentally determine value of weak exchange field in ferromagnets and order parameter of superconductors in this kind of junctions.