Magnetic exchange through s- and d-wave superconductors

Sachio Komori

At a ferromagnet / superconductor interface, a magnetic exchange field can couple with the superconducting state. For the case of an s-wave (isotropic) superconductor, the coupling manifests as a spin-splitting of the superconducting density of states which decays in the superconductor over the Cooper pair coherence length which is tens of nanometers in Nb. In a d-wave (anisotropic) superconductor, the Cooper pair coherence length is spatially anisotropic and sub-nanometre in all directions meaning magnetic coupling is equivalently short ranged. In this talk I will present our recent experiments on investigating magnetic coupling at ferromagnet / superconductor interfaces with s-wave (Nb) and d-wave (YBa2Cu3O7) superconductors. For Nb, superconducting spin-transport based on triplet Cooper pairs is blocked in the singlet superconducting state and rapidly-suppressed in the normal state due to spin-orbit scattering [1]. In YBCO, magnetic exchange field are found to be long-ranged, penetrating tens of coherence lengths due to the quasiparticle nodal states [2]. The results demonstrate dynamic coupling between unconventional superconductivity and magnetism.

[1] S. Komori et al., arXiv:2006.16654
[2] A. Di Bernardo et al., Nat. Mater. 18, 1194 (2019)