The response of fermionic system to external gauge fields is defined by current–current correlation function Πμν(q, q0). Transport properties of different physical quantities are determined by zero energy–momentum limit of it. As it is known close to half-filling the physics of graphene is described by (2+1)-dimensional Dirac theory. In this paper, we calculate current–current correlation function in Dirac theory in a presence of chemical potential η and gap m.
A Self-Consistent Theory of Memory Function in Classical Simple Liquids. II: Dynamical Structure Factor and Current-Current Correlation Function