Superconducting triplet rim currents in a spin-textured ferromagnetic disk

TL;DR

This study demonstrates the emergence of long-range triplet superconductivity localized at the rim of a ferromagnetic disk with a vortex magnetization, driven by spin texture-induced spin-orbit coupling, in Nb/Co Josephson junctions.

Contribution

It reveals that localized rim currents of triplet superconductivity can be induced by spin textures acting as effective spin-orbit coupling in a ferromagnetic disk.

Findings

Long-range triplet currents are localized at the rim of the ferromagnet.

Spin texture acts as an effective spin-orbit coupling leading to spin accumulation.

Both 0 and π channels can be realized by modifying the spin texture.

Abstract

Since the discovery of the long-range superconducting proximity effect, the interaction between spin-triplet Cooper pairs and magnetic structures such as domain walls and vortices has been the subject of intense theoretical discussions, while the relevant experiments remain scarce. We have developed nanostructured Josephson junctions with highly controllable spin texture, based on a disk-shaped Nb/Co bilayer. Here, the vortex magnetization of Co and the Cooper pairs of Nb conspire to induce long-range triplet (LRT) superconductivity in the ferromagnet. Surprisingly, the LRT correlations emerge in highly localized (sub-80 nm) channels at the rim of the ferromagnet, despite its trivial band structure. We show that these robust rim currents arise from the magnetization texture acting as an effective spin-orbit coupling, which results in spin accumulation at the bilayer-vacuum boundary. Lastly, we demonstrate that by altering the spin texture of a single ferromagnet, both $0$ and $\pi$-channels can be realized in the same device.