Thin films of α-MoGe show progressively reduced Tc's as the thickness is decreased below 30 nm and the sheet resistance exceeds 100 Ω/□. We have performed far-infrared transmission and reflection measurements for a set of α-MoGe films to characterize this weakened superconducting state. Our results show the presence of an energy gap with ratio 2Δ0/kBTc=3.8±0.1 in all films studied, slightly higher than the BCS value, even though the transition temperatures decrease significantly as film thickness is reduced. The material properties follow BCS-Eliashberg theory with a large residual scattering rate except that the coherence peak seen in the optical scattering rate is found to be strongly smeared out in the thinner superconducting samples. A peak in the optical mass renormalization at 2Δ0 is predicted and observed for the first time.
@article{arxiv.0803.1185,
title = {The unusual thickness dependence of superconductivity in $\alpha$-MoGe thin films},
author = {H. Tashiro and J. M. Graybeal and D. B. Tanner and E. J. Nicol and J. P. Carbotte and G. L. Carr},
journal= {arXiv preprint arXiv:0803.1185},
year = {2009}
}