Spin-polarized supercurrents for spintronics: a review of current progress

TL;DR

This review discusses the recent progress in creating and understanding long-range spin-polarized supercurrents in superconductor-ferromagnet hybrids, highlighting their potential for advancing super-spintronics and fundamental physics.

Contribution

It summarizes the development of controlled long-range triplet supercurrents and their role in merging superconductivity with spintronics, a new research direction called super-spintronics.

Findings

Triplet supercurrents are now routinely produced and observed since 2010.

Hybrid structures exhibit phenomena like odd-frequency pairing and $ ext{π}$-Josephson junctions.

Advances in nanofabrication enabled exploration of exotic quantum states.

Abstract

During the past 15 years a new field has emerged, which combines superconductivity and spintronics, with the goal to pave a way for new types of devices for applications combining the virtues of both by offering the possibility of long-range spin-polarized supercurrents. Such supercurrents constitute a fruitful basis for the study of fundamental physics as they combine macroscopic quantum coherence with microscopic exchange interactions, spin selectivity, and spin transport. This report follows recent developments in the controlled creation of long-range equal-spin triplet supercurrents in ferromagnets and its contribution to spintronics. The mutual proximity-induced modification of order in superconductor-ferromagnet hybrid structures introduces in a natural way such evasive phenomena as triplet superconductivity, odd-frequency pairing, Fulde-Ferrell-Larkin-Ovchinnikov pairing, long-range equal-spin supercurrents, $\pi$-Josephson junctions, as well as long-range magnetic proximity effects. All these effects were rather exotic before 2000, when improvements in nanofabrication and materials control allowed for a new quality of hybrid structures. Guided by pioneering theoretical studies, experimental progress evolved rapidly, and since 2010 triplet supercurrents are routinely produced and observed. We have entered a new stage of studying new phases of matter previously out of our reach, and of merging the hitherto disparate fields of superconductivity and spintronics to a new research direction: super-spintronics.