Long-range spin current driven by superconducting phase difference in a Josephson junction with double layer ferromagnets

TL;DR

This paper theoretically demonstrates that a long-range spin current can be generated and sustained in a Josephson junction with double-layer ferromagnets by the superconducting phase difference, driven by spin-triplet Cooper pairs.

Contribution

It introduces a novel mechanism for long-range spin current in Josephson junctions driven solely by phase difference, highlighting potential for spintronics applications.

Findings

Long-range spin current driven by phase difference without voltage.

Spin-triplet Cooper pairs enable long-distance spin transport.

Spin current persists over longer distances than conventional spin currents.

Abstract

We theoretically study spin current through ferromagnet (F) in a Josephson junction composed of s-wave superconductors and two layers of ferromagnets. Using quasiclassical theory, we show that the long-range spin current can be driven by the superconducting phase difference without voltage drop. The origin of this spin current is due to spin-triplet Cooper pairs (STCs) formed by electrons of equal-spin, which are induced by proximity effect inside the F. We find that the spin current carried by the STCs exhibits long-range propagation in the F even where the Josephson charge current is practically zero. We also show that this spin current persists over a remarkably longer distance than the ordinary spin current carried by spin polarized conduction electrons in the F. Our results thus indicate the promising potential of Josephson junctions based on multilayer ferromagnets for spintronics applications with long-range propagating spin current.