Observation of spin-triplet superconductivity in Co-based Josephson Junctions

TL;DR

This paper reports the experimental observation of long-range spin-triplet superconductivity in Co-based Josephson junctions with weakly ferromagnetic alloy layers, demonstrating controllable supercurrents due to induced triplet pair correlations.

Contribution

It provides the first experimental evidence of spin-triplet pairing in Co-based junctions with alloy layers, confirming theoretical predictions.

Findings

Long-range supercurrent observed in Co junctions with alloy layers

Supercurrent decay is suppressed by alloy layer insertion

Supercurrent is tunable by alloy layer thickness

Abstract

We have measured a long-range supercurrent in Josephson junctions containing Co (a strong ferromagnetic material) when we insert thin layers of either PdNi or CuNi weakly-ferromagnetic alloys between the Co and the two superconducting Nb electrodes. The critical current in such junctions hardly decays for Co thicknesses in the range of 12-28 nm, whereas it decays very steeply in similar junctions without the alloy layers. The long-range supercurrent is controllable by the thickness of the alloy layer, reaching a maximum for a thickness of a few nm. These experimental observations provide strong evidence for induced spin-triplet pair correlations, which have been predicted to occur in superconducting/ferromagnetic hybrid systems in the presence of certain types of magnetic inhomogeneity.