Electron-phonon interaction in graphite intercalation compounds

Motivated by the recent discovery of superconductivity in Ca- and Yb-intercalated graphite (CaC6 and YbC6) and from the ongoing debate on the nature and role of the interlayer state in this class of compounds, in this work we critically study the electron-phonon properties of a simple model based on primitive graphite. We show that this model captures an essential feature of the electron-phonon properties of the graphite intercalation compounds, namely, the existence of a strong dormant electron-phonon interaction between interlayer and pi(*) electrons, for which we provide a simple geometrical explanation in terms of Wannier-like functions. Our findings correct the oversimplified view that nearly free-electron states cannot interact with the surrounding lattice and explain the empirical correlation between the filling of the interlayer band and the occurrence of superconductivity in graphite intercalation compounds.