Josephson effect and spin-triplet pairing correlations in SF <inf>1</inf>F<inf>2</inf>S junctions

Abstract

We study theoretically the Josephson effect and pairing correlations in planar SF1F2S junctions that consist of conventional superconductors (S) connected by two metallic monodomain ferromagnets (F 1 and F2) with transparent interfaces. We obtain both spin-singlet and -triplet pair amplitudes and the Josephson current-phase relations for arbitrary orientation of the magnetizations using the self-consistent solutions of Eilenberger equations in the clean limit and for a moderate disorder in ferromagnets. We find that the long-range triplet correlations cannot prevail in symmetric junctions with equal ferromagnetic layers. Surprisingly, the long-range spin-triplet correlations give the dominant second harmonic in the Josephson current-phase relation of highly asymmetric SF1F2S junctions. The effect is robust against moderate disorder and variations in the layers thickness and exchange energy of ferromagnets. © 2011 American Physical Society.