Enhanced flux expulsion in superconductor-ferromagnet proximity coupled systems.

In mesoscopic systems the Meissner response of a superconducting film can be very different from its bulk behaviour. In normal (N) superconductor (S) bilayer systems screening can be greatly enhanced depending on the relative material properties and interface conditions¹. Furthermore, with the addition of ferromagnetic (F) layers comes the possibility of generating a paramagnetic screening response due to spin triplet pairs². Such modifications to the screening manifest in the flux profile across the sample which we can directly probe using Low energy muon spin spectroscopy (LE-μSR)³. We present our recent LE-μSR results on bi and trilayer systems of N, S and F layers. We find the expected NS bilayer enhancement which can be modelled successfully in the Quasiclassical framework. A large discrepancy between experiment and theory occurs, however, with the addition of an F layer. In this case we find a further unexpected enhancement to the flux profile. The F layer enhancement can be tuned by modifying the interface conditions. This work is valuable for understanding more complex S, F, N systems in which there is much interest.

¹Belzig et. al., PRB 53, 5727 (1996)
²Alidoust et. al., PRB 89, 054508 (2014)
³Di Bernadino et. al., PRX 5, 041021 (2015)