Interplay of spin-discriminated Andreev bound states forming the 0-π transition in superconductor-ferromagnet-superconductor junctions -: art. no. 144502

The Josephson current in superconductor-ferromagnet-superconductor junctions is described by taking into account different reflection (transmission) amplitudes for quasiparticles with spin up and down. We show that the 0-pi transition in the junctions can take place at some temperature only for sufficiently strong spin activity of the interface. In particular, Andreev interface bound-state energies in one spin channel have to be all negative, while in the other one positive. Only one spin channel contributes then to the zero-temperature Josephson current. At the temperature of the 0-pi transition two channels can substantially compensate each other forming a pronounced minimum in the critical current in tunnel junctions. The Josephson current at that temperature is quadratic in small transparency and the current-phase relation contains first and second harmonics of one and the same order.