Supercurrents in ferromagnets

Abstract

The deeply antagonistic electronic properties of superconductors and ferromagnets give rise to a tough question: what happens to the electron spins of superconducting Cooper pairs at the interface between a superconductor and a ferromagnet? The question poses two experimental challenges. First, in principle there is the need to know the local electronic properties at the interface to a level comparable to that reached in semiconductor heterostructures. Second, there is also a need to identify experimental Cooper-pair-related observables that depend on these interfacial properties. One outstanding property is the observation of a supercurrent through a ferromagnet over a given length, which is incompatible with the standard spin-singlet Cooper pairs. It is called the long-range proximity (LRP) effect. After a few previous indications, the evidence for such an LRP effect is now becoming rapidly stronger with the publication in Nature Physics of a paper by Jian Wang et al., one of the first reports to describe this effect.