Field theoretic renormalization study of interaction corrections to the universal ac conductivity of graphene

The two-loop interaction correction coefficient to the universal ac conductivity of disorder-free intrinsic graphene is computed with the help of a field theoretic renormalization study using the Bogoliubov-Parasiuk-Hepp-Zimmermann prescription. Non-standard Ward identities imply that divergent subgraphs (related to Fermi velocity renormalization) contribute to the renormalized optical conductivity. Proceeding either via densitydensity or via current-current correlation functions, a single well-defined value is obtained: C=.(19-6π )/12)=0.01 in agreement with the result first obtained by Mishchenko and which is compatible with experimental uncertainties.