title: Measurement of the optical conductivity of graphene.
abstract: Optical reflectivity and transmission measurements over photon energies between 0.2 and 1.2 eV were performed on single-crystal graphene samples on a SiO2 substrate. For photon energies above 0.5 eV, graphene yielded a spectrally flat optical absorbance of (2.3+/-0.2)%. This result is in agreement with a constant absorbance of pialpha, or a sheet conductivity of pie2/2h, predicted within a model of noninteracting massless Dirac fermions. This simple result breaks down at lower photon energies, where both spectral and sample-to-sample variations were observed. This "nonuniversal" behavior is explained by including the effects of doping and finite temperature, as well as contributions from intraband transitions.
authors.affiliation: Department of Physics, Columbia University, 538 West 120th Street, New York, New York 10027, USA.
authors.forename: Kin Fai
authors.initials: KF
authors.lastname: Mak
authors.forename: Matthew Y
authors.initials: MY
authors.lastname: Sfeir
authors.forename: Yang
authors.initials: Y
authors.lastname: Wu
authors.forename: Chun Hung
authors.initials: CH
authors.lastname: Lui
authors.forename: James A
authors.initials: JA
authors.lastname: Misewich
authors.forename: Tony F
authors.initials: TF
authors.lastname: Heinz