Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 11: C/diamond

HL 11.3: Vortrag

Montag, 25. Februar 2008, 11:30–11:45, EW 202

Molecular doping and pseudo Landau levels in graphene — •Tim Wehling and Alexander Lichtenstein — I. Institut für Theoretische Physik, Universität Hamburg, 20355 Hamburg, Germany

Controlling graphene’s density of states near the Fermi level is crucial for future applications based on this material. Two mechanisms related to this goal will be addressed, here. Firstly, we present a joint experimental and ab-initio theoretical investigation of adsorbate induced doping of graphene. A general relation between the doping strength and whether or not adsorbates are open- or closed- shell systems is demonstrated with the NO₂-system: The single, open shell NO₂ molecule is found to be a strong acceptor, whereas its closed shell dimer N₂O₄ causes only weak doping. This effect is pronounced by graphene’s peculiar density of states (DOS), which is ideal for chemical sensor applications. We explain the recently observed [Schedin et. al., Nat. Mater 6, 652 (2007)] NO₂ single molecule detection.

In addition, we present first principles calculations on midgap states in corrugated graphene: Rippling induces pseudomagnetic fields leading to the formation of flat bands near the Fermi level — so-called pseudo-Landau levels. Especially, the chiral zero-energy pseudo-Landau level gives rise to specific real space signatures like full sublattice polarization and related sublattice stripes observable in any experiment probing the local electronic structure.

In collaboration with A. Balatsky (LANL), A. Geim (U. Manchester), M. Katsnelson (U. Nijmegen) and K. Novoselov (U. Manchester).