title: Renormalization of the graphene dispersion velocity determined from scanning tunneling spectroscopy.
abstract: In graphene, as in most metals, electron-electron interactions renormalize the properties of electrons but leave them behaving like noninteracting quasiparticles. Many measurements probe the renormalized properties of electrons right at the Fermi energy. Uniquely for graphene, the accessibility of the electrons at the surface offers the opportunity to use scanned probe techniques to examine the effect of interactions at energies away from the Fermi energy, over a broad range of densities, and on a local scale. Using scanning tunneling spectroscopy, we show that electron interactions leave the graphene energy dispersion linear as a function of excitation energy for energies within ±200  meV of the Fermi energy. However, the measured dispersion velocity depends on density and increases strongly as the density approaches zero near the charge neutrality point, revealing a squeezing of the Dirac cone due to interactions.
authors.affiliation: Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: Jungseok
authors.initials: J
authors.lastname: Chae
authors.forename: Suyong
authors.initials: S
authors.lastname: Jung
authors.forename: Andrea F
authors.initials: AF
authors.lastname: Young
authors.forename: Cory R
authors.initials: CR
authors.lastname: Dean
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Yuanda
authors.initials: Y
authors.lastname: Gao
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Shepard
authors.forename: Phillip
authors.initials: P
authors.lastname: Kim
authors.forename: Nikolai B
authors.initials: NB
authors.lastname: Zhitenev
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Stroscio