Regensburg 2013 – scientific programme
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O: Fachverband Oberflächenphysik
O 23: Graphene: Electronic Properties and Transport (jointly with HL, MA and TT)
O 23.9: Talk
Monday, March 11, 2013, 18:00–18:15, H17
Intact Dirac cones at broken sublattice symmetry: photoemission study of graphene on Ni and Co — •Dmitry Marchenko1, Andrei Varykhalov1, Jaime Sánchez-Barriga1, Markus R. Scholz1, Bart Verberck2, Björn Trauzettel3, Tim O. Wehling4,5, Carlo Carbone6, and Oliver Rader1 — 1Helmholtz-Zentrum Berlin — 2Universiteit Antwerpen — 3Universität Würzburg — 4Universität Bremen — 5Bremen Center for Computational Materials Science — 6Consiglio Nazionale delle Ricerche Trieste
A band gap at the Dirac point of graphene can be created by breaking of the sublattice symmetry through epitaxial growth on a substrate crystal. One of the strongest sublattice-symmetry-breaking interactions with predicted and measured band gaps ranging from 400 meV to more than 3 eV has been attributed to the interfaces of graphene with Ni and Co, which are also promising spin filter interfaces. We apply angle-resolved photoemission to epitaxial graphene on Ni(111) and Co(0001) to show the presence of intact Dirac cones in a strongly n-doped system. Our results challenge the common belief that breaking of sublattice symmetry by a substrate and opening of the band gap at the Dirac energy are in a straightforward relation. A simple effective model of a biased bilayer structure composed of graphene and a sublattice symmetry broken layer, corroborated by density functional theory calculations, demonstrates the general validity of our conclusions.