Electronic structure and electron-phonon coupling of doped graphene layers in KC8

We propose graphite intercalation compounds (GICs) as a material system with precisely the same electronic properties as doped few layer graphene. Despite the fact that GICs have been around for the last four decades, this fact has gone unnoticed so far. Especially, we focus on the electronic energy bands of ${\text{KC}}_{8}$ which correspond to a doped graphene monolayer. We provide extensive theoretical and experimental evidence for this claim employing a combined angle-resolved photoemission and theory approach using tight-binding, standard density-functional theory and including electron-electron correlation on a $GW$ level. We observe a strong momentum-dependent kink in the quasiparticle dispersion at 166 meV highlighting electron-phonon coupling to an in-plane transversal optical phonon. These results are key for understanding both the unique electronic properties of doped graphene layers and superconductivity in ${\text{KC}}_{8}$.