Electrons in isolated graphene layers are a two-dimensional gas of massless Dirac Fermions. In realistic devices, however, the electronic properties are modified by elastic deformations, interlayer coupling and substrate interaction. Here we unravel the electronic structure of doped graphene, revisiting the stage one graphite intercalation compound KC8 using angle--resolved photoemission spectroscopy and ab--initio calculations. The full experimental dispersion is in excellent agreement to calculations of doped graphene once electron correlations are included on the GW level. This highlights that KC8 has negligible interlayer coupling. Therefore Dirac Fermion behaviour is preserved and we directly determine the full experimental Dirac cone of doped graphene. In addition we prove that superconductivity in KC8 is mediated by electron--phonon coupling to an iTO phonon, yielding a strong kink in the quasiparticle dispersion at 166 meV. These results are key for understanding, both, the unique electronic properties of graphene and superconductivity in KC8.
@article{arxiv.0808.1613,
title = {Graphite intercalation compound KC$_8$ revisited: a key to graphene},
author = {A. Grüneis and C. Attaccalite and A. Rubio and D. Vyalikh and S. L. Molodtsov and J. Fink and R. Follath and W. Eberhardt and B. Büchner and T. Pichler},
journal= {arXiv preprint arXiv:0808.1613},
year = {2009}
}