Supercurrent in ferromagnetic Josephson junctions with heavy metal interlayers

TL;DR

This paper investigates how adding heavy metal interlayers, specifically platinum, affects supercurrent transmission in ferromagnetic Josephson junctions, revealing enhanced supercurrent but unchanged decay length, with implications for superspintronics.

Contribution

It introduces spin-orbit coupling layers as a new mechanism for singlet-triplet conversion in Josephson junctions and demonstrates their effect on supercurrent transmission.

Findings

Supercurrent transmission increases with Pt layers.

Decay length of supercurrent remains unchanged.

Pt acts as a buffer layer improving Co layer growth.

Abstract

The lengthscale over which supercurrent from conventional BCS, $s$-wave, superconductors ($S$) can penetrate an adjacent ferromagnetic ($F$) layer depends on the ability to convert singlet Cooper pairs into triplet Cooper pairs. Spin aligned triplet Cooper pairs are not dephased by the ferromagnetic exchange interaction, and can thus penetrate an $F$ layer over much longer distances than singlet Cooper pairs. These triplet Cooper pairs carry a dissipationless spin current and are the fundamental building block for the fledgling field of superspintronics. Singlet-triplet conversion by inhomogeneous magnetism is well established. Here, we describe an attempt to use spin orbit coupling as a new mechanism to mediate singlet-triplet conversion in $S-F-S$ Josephson junctions. We report that the addition of thin Pt spin-orbit coupling layers in our Josephson junctions significantly increases supercurrent transmission, however the decay length of the supercurrent is not found to increase. We attribute the increased supercurrent transmission to Pt acting as a buffer layer to improve the growth of the Co $F$ layer.