Interplay of spin-discriminated Andreev bound states forming the 0−π transition in superconductor-ferromagnet-superconductor junctions

Yu. S. Barash; I. V. Bobkova

doi:10.1103/PhysRevB.65.144502

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Interplay of spin-discriminated Andreev bound states forming the 0−π transition in superconductor-ferromagnet-superconductor junctions

Yu. S. Barash, I. V. Bobkova

DOI 10.1103/PhysRevB.65.144502 · Physical Review B

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Abstract

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−π 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−π 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.