We have experimentally investigated the density of states (DOS) in Nb/Ni (S/F) bilayers as a function of Ni thickness, dF. Our thinnest samples show the usual DOS peak at ±Δ0, whereas intermediate-thickness samples have an anomalous ``double-peak'' structure. For thicker samples (dF≥3.5 nm), we see an ``inverted'' DOS which has previously only been reported in superconductor/weak-ferromagnet structures. We analyze the data using the self-consistent non-linear Usadel equation and find that we are able to quantitatively fit the features at ±Δ0 if we include a large amount of spin-orbit scattering in the model. Interestingly, we are unable to reproduce the sub-gap structure through the addition of any parameter(s). Therefore, the observed anomalous sub-gap structure represents new physics beyond that contained in the present Usadel theory.
@article{arxiv.0712.1322,
title = {Anomalous double peak structure in Nb/Ni superconductor/ferromagnet tunneling DOS},
author = {P. SanGiorgio and S. Reymond and M. R. Beasley and J. H. Kwon and K. Char},
journal= {arXiv preprint arXiv:0712.1322},
year = {2009}
}