title: Chirality-induced dynamic kohn anomalies in graphene.
abstract: We develop a theory for the renormalization of the phonon energy dispersion in graphene due to the combined effects of both Coulomb and electron-phonon (e-ph) interactions. We obtain the renormalized phonon energy spectrum by an exact analytic derivation of the phonon self-energy, finding three distinct Kohn anomalies (KAs) at the phonon wave vector q=omega/v, 2k_{F}+/-omega/v for LO phonons and one at q=omega/v for TO phonons. The presence of these new KAs in graphene, in contrast to the usual KA q=2k_{F} in ordinary metals, originates from the dynamical screening of e-ph interaction (with a concomitant breakdown of the Born-Oppenheimer approximation) and the peculiar chirality of the graphene e-ph coupling.
authors.affiliation: Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Wang-Kong
authors.initials: WK
authors.lastname: Tse
authors.forename: Ben Yu-Kuang
authors.initials: BY
authors.lastname: Hu
authors.forename: S
authors.initials: S
authors.lastname: Das Sarma