Recently deiscovered superconductivity in YbC6 and CaC6 at temperatures substantially higher than previously known for intercalated graphites, raised several new questions: (1) Is the mechanism considerably different from the previously known intercalated graphites? (2) If superconductivity is conventional, what are the relevant phonons? (3) Given extreme similarity between YbC6 and CaCa6, why their critical temperatures are so different? We address these questions on the basis of first-principles calculations and conclude that coupling with intercalant phonons is likely to be the main force for superconductivity in YbC6 and CaC6, but not in alkaline-intercalated compounds, and explain the difference in Tc by the ``isotope effect'' due to the difference in Yb and Ca atomic masses.
@article{arxiv.cond-mat/0504127,
title = {Intercalant-Driven Superconductivity in YbC$_{6}$ and CaC$_{6}$},
author = {I. I. Mazin},
journal= {arXiv preprint arXiv:cond-mat/0504127},
year = {2009}
}