In most metals, electrons behave as non-interacting quasiparticles with renormalized dynamical properties in the presence of electron interactions. Historically, many measurements are capable to probe the effect of interactions at the Fermi energy. Graphene, with its carriers being exposed at the surface and the continuous tunability of carriers from electrons to holes, offers a unique opportunity to examine interaction physics at arbitrary energies over a broad range of density, and on a local scale. Here we show that in the presence of interactions, the graphene energy dispersion remains linear as a function of excitation energy and can be described by a momentum independent dispersion velocity for any measured density. However, the measured dispersion velocity is density dependent, and strongly increases as the charge neutrality point is approached. The preservation of the linear spectrum with the renormalization of the dispersion velocity with density reveals a squeezing of the Dirac cone angle due to electron interactions at low densities.
Citation: Physical Review Letters
Pub Type: Journals
graphene, velocity, scanning tunneling microscopy, scanning tunneling spectroscopy