Renormalization of graphene bands by many-body interactions

We have determined the electronic bandstructure of clean and potassium-doped single layer graphene, and fitted the graphene pi bands to a first- and third-nearest-neighbor tight binding model. We characterized the quasiparticle dynamics using angle resolved photoemission spectroscopy. The dynamics reflect the decay of quasiparticles (holes) into collective excitations, namely plasmons, phonons, and electron-hole pairs. Electron-hole pair decay is found to be a minimum at the Dirac energy E-D while electron-plasmon scattering is maximum around the same energy. Taking the topology of the bands around the Dirac energy for n-doped graphene into account, we show that these results follow from kinematic constraints imposed by graphene's gapless energy spectrum around the Dirac energy. We also show that the electron-phonon scattering in lightly doped graphene is around 6 times larger than the predictions of published calculations. (c) 2007 Published by Elsevier Ltd.