Schedule Feb 12, 2010
What Is the Fine Structure Constant of Graphene?
Peter Abbamonte (UIUC)

Electrons in graphene behave like relativistic, Dirac Fermions, permitting phenomena in high energy physics to be studied in a solid state setting. A key question is whether these fermions are noninteracting, or if their properties are critically influenced by Coulomb correlations. We performed inelastic x-ray scattering experiments on single crystals of graphite, and applied state-of-the-art reconstruction algorithms to image the dynamical screening of a point charge in an isolated, graphene sheet. We found that an electron in graphene is dressed by cloud of charge, approximately 1 nm in size, that arises from two van Hove singularities residing beyond the Dirac spectrum. This cloud renormalizes the electron charge to e*=(0.070+/-0.043)e, and the fine structure constant to 0.15+/-0.092. Our result explains the absence of correlation anomalies in several spectroscopic experiments, and suggests that correlations have a weak influence on long-wavelength phenomena, such as the transport of current in zero magnetic field.

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