Josephson effect and spin-triplet pairing correlations in SF1F2S junctions

TL;DR

This paper theoretically investigates the Josephson effect and pairing correlations in SF1F2S junctions, revealing the dominance of long-range spin-triplet correlations in asymmetric configurations and their robustness against disorder.

Contribution

It provides a self-consistent analysis of spin-triplet and singlet correlations and Josephson current relations in SF1F2S junctions with arbitrary magnetization orientations.

Findings

Long-range spin-triplet correlations are suppressed in symmetric junctions.

Asymmetric junctions exhibit a dominant second harmonic due to triplet correlations.

The effects are robust against moderate disorder and layer variations.

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 (F1 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 spin-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.