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 ππ 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 ED while electron–plasmon scattering is maximum around the same energy. Taking the topology of the bands around the Dirac energy for nn-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.