Peculiar long-range supercurrent in SFS junction containing a noncollinear magnetic domain in the ferromagnetic region

TL;DR

This paper investigates a superconductor-ferromagnet-superconductor junction with a noncollinear magnetic domain, revealing a novel long-range supercurrent mechanism driven mainly by singlet Cooper pairs rather than triplet pairs.

Contribution

It demonstrates a new mechanism for long-range supercurrent involving phase cancellation and spin-flip processes in a magnetic domain, differing from traditional triplet-based explanations.

Findings

Magnetic domain induces spin-flip, reversing Cooper pair spins.

Long-range supercurrent arises mainly from singlet pairs, not triplet.

Equal spin triplet pairs are confined to the magnetic domain region.

Abstract

We study the supercurrent in a superconductor-ferromagnet-superconductor heterostructure containing a noncollinear magnetic domain in the ferromagnetic region. It is demonstrated that the magnetic domain can lead to a spin-flip process, which can reverse the spin orientations of the singlet Cooper pair propagating through the magnetic domain region. If the ferromagnetic layers on both sides of magnetic domain have the same features, the long-range proximity effect will take place. That is because the singlet Cooper pair will create an exact phase-cancellation effect and gets an additional $\pi$ phase shift as it passes through the entire ferromagnetic region. Then the equal spin triplet pair only exists in the magnetic domain region and can not diffuse into the other two ferromagnetic layers. So the supercurrent mostly arises from the singlet Cooper pairs and the equal spin triplet pairs are not involved. This behavior is quite distinct from the common knowledge that long-range supercurrent induced by inhomogeneous ferromagnetism stems from the equal spin triplet pairs. The result we presented here provides a new way for generating the long-range supercurrent.