Spin-triplet supercurrent in Josephson junctions containing a synthetic antiferromagnet with perpendicular magnetic anisotropy

TL;DR

This paper demonstrates spin-triplet supercurrent in Josephson junctions with a synthetic antiferromagnet and multiple magnetic layers, showing slower decay of supercurrent with thickness, indicating triplet pairing.

Contribution

It introduces a new Josephson junction design with noncolinear magnetic layers that supports spin-triplet supercurrent, advancing understanding of triplet superconductivity in magnetic structures.

Findings

Supercurrent decays more slowly with $F$-layer thickness in these junctions.

Supercurrent is carried by spin-triplet pairs, confirmed by decay behavior.

Permalloy layers enable control of critical current and phase difference.

Abstract

We present measurements of Josephson junctions containing three magnetic layers with noncolinear magnetizations. The junctions are of the form $S/F^{\prime}/N/F/N/F^{\prime \prime}/S$, where $S$ is superconducting Nb, $F^\prime$ is either a thin Ni or Permalloy layer with in-plane magnetization, $N$ is the normal metal Cu, $F$ is a synthetic antiferromagnet (SAF) with magnetization perpendicular to the plane, composed of Pd/Co multilayers on either side of a thin Ru spacer, and $F^{\prime \prime}$ is a thin Ni layer with in-plane magnetization. The supercurrent in these junctions decays more slowly as a function of the $F$-layer thickness than for similar spin-singlet junctions not containing the $F^\prime$ and $F^{\prime \prime}$ layers. The slower decay is the prime signature that the supercurrent in the central part of these junctions is carried by spin-triplet pairs. The junctions containing $F^{\prime}=$ Permalloy are suitable for future experiments where either the amplitude of the critical current or the ground-state phase difference across the junction is controlled by changing the relative orientations of the magnetizations of the $F^{\prime}$ and $F^{\prime \prime}$ layers.