Electronic structure of potassium graphite intercalation compounds KC8 and KC24

The recent discovery of high superconducting transitions in graphite intercalation compounds has sparked a new wave of interest in these materials. We report angle-resolved photoemission spectroscopy study of the first and second stage of graphite intercalated with potassium: KC8 and KC24. In both compounds, a complete charge transfer from the alkali metal to the graphene sheets was observed. Electron-phonon coupling on graphene-derived p* states with in-plane graphene-derived phonons is stronger in KC8, following a universal trend observed in other alkaline intercalated compounds where the coupling strengthens with doping of p* states. The observed coupling is therefore a good candidate for pairing interaction that causes superconductivity in graphite intercalation compounds.