Measurement of the optical conductivity of graphene.
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.
Mak
Kin Fai
KF
Department of Physics, Columbia University, 538 West 120th Street, New York, New York 10027, USA.
Sfeir
Matthew Y
MY
Wu
Yang
Y
Lui
Chun Hung
CH
Misewich
James A
JA
Heinz
Tony F
TF