Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 51: Graphene III

O 51.8: Talk

Wednesday, March 16, 2011, 16:45–17:00, WIL B321

Plasmarons in Quasi-Freestanding Doped Graphene Observed through Photoemission — Aaron Bostwick¹, Florian Speck², Thomas Seyller², •Karsten Horn³, Marco Polini⁴, Reza Asgari⁵, Allan McDonald⁶, and Eli Rotenberg¹ — ¹ALS, Lawrence Berkeley Lab, USA — ²Technische Physik, Uni Erlangen, Germany — ³Fritz Haber Institute, Max Planck Society, Berlin, Germany — ⁴CNR and Scuola Normale Superiore Pisa, Italy — ⁵Institute of Research in Fundamental Sciences, Teheran, Iran — ⁶Department of Physics, University of Texas, Austin USA

The unusual conical band structure of graphene leads to a zero-energy band gap at a single Dirac crossing point. By measuring the spectral function of charge carriers in quasi-freestanding graphene with ARPES, we showe that at finite doping, this well-known linear Dirac spectrum does not provide a full description of the charge-carrying excitations. We observed composite plasmaron particles, which are bound states of charge carriers with plasmons, the density oscillations of the graphene electron gas; such quasiparticles were predicted more than forty years ago, but their experimental confirmation so far has proven elusive. We show that the Dirac crossing point is resolved into three crossings: the first between pure charge bands, the second between pure plasmaron bands, and the third a ring-shaped crossing between charge and plasmaron bands. This observation resolves a controversy about the existence of a gap at the Dirac point in graphene on SiC(0001).