Virtual Photon Contribution to Frictional Drag in double-layer Devices
  The first order contribution to frictional drag in bi-layered fermion gas is examined. We discuss the relevance of single photon exchange in the evaluation of transresistance, which is usually explained by second order effects such as Coulomb and phonon drag. Since the effective e.m. interaction is unscreened, in the d.c. limit we obtain a finite (and large) contribution to transconductivity. 
A. Donarini, R. Ferrari, A. P. Jauho and L. Molinari