The Effective Fine-Structure Constant of Freestanding Graphene Measured in Graphite

Science  05 Nov 2010:
Vol. 330, Issue 6005, pp. 805-808
DOI: 10.1126/science.1190920

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Electrons in graphene behave like Dirac fermions, permitting phenomena from high-energy physics to be studied in a solid-state setting. A key question is whether or not these fermions are critically influenced by Coulomb correlations. We performed inelastic x-ray scattering experiments on crystals of graphite and applied reconstruction algorithms to image the dynamical screening of charge in a freestanding graphene sheet. We found that the polarizability of the Dirac fermions is amplified by excitonic effects, improving screening of interactions between quasiparticles. The strength of interactions is characterized by a scale-dependent, effective fine-structure constant, αg*(k,ω), the value of which approaches 0.14±0.092~1/7 at low energy and large distances. This value is substantially smaller than the nominal αg=2.2, suggesting that, on the whole, graphene is more weakly interacting than previously believed.

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