Spin-triplet supercurrents in lateral superconductor/ferromagnet Josephson junctions

Huygens - Kamerlingh Onnes Laboratory, Leiden University

The phenomenon of s-wave spin triplet Cooper pairs induced in ferromagnetic metals, leading to spin-polarized supercurrents, has been researched now for more than a decade. Its main aspects are well understood: crucial in converting s-wave singlet pairs in the superconductor (S) to s-wave triplets in the ferromagnet (F) is the engineering of a controlled magnetic inhomogeneity at the S/F interface. Much used for this is a layer stack wirh two different ferromagnets that have non-collinear magnetization. However, other kinds of magnetic textures are possible that have been much less investigated. After a brief introduction into ‘S/F physics’, I will review experiments on lateral disk-shaped Josephson junctions, where the physics is largely determined by the vortex magnetization of the ferromagnetic disk. A particularly interesting finding is that the supercurrent distribution in such disks is strongly peaked at the rims of the device. The materials we use are mainly Nb, Ni and Co, but recent results on long range proximity effects in the halfmetallic ferromagnetic oxide La_0.7Sr_0.3MnO₃ will also be presented.