Superfluid Densities in Superconducting/Ferromagnetic (Nb/NiV/Nb) Heterostructures

Superfluid density measurements allow us to probe the superconducting structure of thin films below T$_{c}$ with remarkable detail. They yield information not only of the inherent robustness of the superconducting state, but also about the homogeneity of the sample and possible ``hidden'' transitions at temperatures lower than the initial T$_{c}$. For this reason multiple transitions in superconducting heterostructures are revealed to us. We use superfluid density measurements on Nb/Ni$_{0.95}$V$_{0.05}$/Nb trilayers to study the interplay between two superconducting films separated by the destructive proximity effects of a ferromagnet. We show there are trilayers with strong coupling, which produces a single transition, that become decoupled to the point of separation into two transitions as the ferromagnetic layer thickness increases. We discuss the difficulties in observing the second transition in $\sigma _{1}$, while obvious in $\lambda ^{-2}$.