▎ 摘　　要

The effectively massless, relativistic behaviour of graphene's charge carriers-known as Dirac fermions-is a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). The study of many-body interactions amongst the charge carriers in graphene and related systems such as carbon nanotubes, fullerenes and graphite is of interest owing to their contribution to superconductivity and other exotic ground states in these systems. Here we show, using angle-resolved photoemission spectroscopy, that electron-plasmon coupling plays an unusually strong role in renormalizing the bands around the Dirac crossing energy-analogous to mass renormalization by electron-boson coupling in ordinary metals. Our results show that electron-electron, electron-plasmon and electron-phonon coupling must be considered on an equal footing in attempts to understand the dynamics of quasiparticles in graphene and related systems.