Tunneling density of states as a function of thickness in superconductor/strong ferromagnet bilayers

We have made an experimental study of the tunneling density of states (DOS) in strong ferromagnetic thin films (CoFe) in proximity with a thick superconducting film (Nb) as a function of the ferromagnetic thickness d(F). Remarkably, we find that as d(F) increases, the superconducting DOS exhibits a scaling behavior in which the deviations from the normal-state conductance have a universal shape, which decreases exponentially in amplitude. The decay length d(1) is approximately 0.4 nm. We do not see oscillations in the DOS as a function of d(F), as one would expect from predictions based on the Usadel equations using reasonable parameters.