Effective Fine-Structure Constant of Freestanding Graphene Measured in Graphite

• Published in: Science (American Association for the Advancement of Science) Vol. 330; no. 6005; pp. 805 - 808
• Main Authors: Reed, James P, Uchoa, Bruno, Joe, Young Il, Gan, Yu, Casa, Diego, Fradkin, Eduardo, Abbamonte, Peter
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 05.11.2010; The American Association for the Advancement of Science
• Subjects: Algorithms; Charge; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Crystal structure; Crystals; Dielectric materials; Electron density; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic structure of nanoscale materials : clusters, nanoparticles, nanotubes, and nanocrystals; Electrons; Exact sciences and technology; Fermions; Graphene; Graphite; Impurities; Inelastic scattering; Momentum; Physics; Plasmons; Reconstruction; Screening; Spectral bands; Texts; X-rays; Fine structure; Screening; X-ray scattering; Inelastic scattering; Impurities; Graphene; Graphite; Free-standing film; Response functions; Dirac particle; Coulomb interaction
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1190920

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, [Formula: see text], the value of which approaches [Formula: see text] at low energy and large distances. This value is substantially smaller than the nominal [Formula: see text], suggesting that, on the whole, graphene is more weakly interacting than previously believed.