We have measured the Ca isotope effect in the newly discovered superconductor CaC6. The isotope effect coefficient is 0.50(7). If one assumes that this material is a conventional electron-phonon coupled superconductor, this result shows that the superconductivity is dominated by coupling of the electrons by Ca phonon modes and that C phonons contribute very little. Thus, in contrast to MgB2, where phonons in the B layers are responsible for the superconductivity, in CaC6 the phonons are primarily modes of the intercalated Ca.
Cite
@article{arxiv.cond-mat/0604642,
title = {Large Ca Isotope Effect in CaC6},
author = {D. G. Hinks and D. Rosenmann and H. Claus and M. S. Bailey and J. D. Jorgensen},
journal= {arXiv preprint arXiv:cond-mat/0604642},
year = {2015}
}