title: Non-equilibrium Dirac carrier dynamics in graphene investigated with time- and angle-resolved photoemission spectroscopy.
abstract: We have used time- and angle-resolved photoemission spectroscopy (tr-ARPES) to assess the influence of many-body interactions on the Dirac carrier dynamics in graphene. From the energy-dependence of the measured scattering rates we directly determine the imaginary part of the self-energy, visualizing the existence of a relaxation bottleneck associated with electron-phonon coupling. A comparison with static line widths obtained by high-resolution ARPES indicates that the dynamics of photo-excited carriers in graphene are solely determined by the equilibrium self-energy. Furthermore, the subtle interplay of different many-body interactions in graphene may allow for carrier multiplication, where the absorption of a single photon generates more than one electron-hole pair via impact ionization. We find that, after photo-excitation, the number of carriers in the conduction band along the ΓK-direction keeps increasing for about 40 fs after the pump pulse is gone. A definite proof of carrier multiplication in graphene, however, requires a more systematic study, carefully taking into account the contribution of momentum relaxation on the measured rise time.
authors.affiliation: Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany. isabella.gierz@mpsd.mpg.de.
authors.forename: Isabella
authors.initials: I
authors.lastname: Gierz
authors.forename: Stefan
authors.initials: S
authors.lastname: Link
authors.forename: Ulrich
authors.initials: U
authors.lastname: Starke
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavalleri