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 π^* 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.