Charge transfer and electronic structure of graphene and graphite intercalation compounds

In graphite intercalation compounds (GIC), layers of different chemical species (intercalants) are introduced between graphene sheets. Due to the charge transfer between the intercalant and graphene layers, intercalation allows a controlled doping of graphene sheets and a broad variation of many physical properties, including the emergence of relatively high transition temperature superconductivity in some GICs. We have studied the changes in the electronic structure of various GICs in angle-resolved photoemission spectroscopy and found that, with the doping of graphene sheets, the electronic correlations become stronger and more anisotropic. In particular, the electron phonon coupling of graphene-derived electronic states with high-frequency graphene-derived vibrations increases dramatically with the amount of charge transfer.