Würzburg Seminar on Quantum Field Theory and Gravity

In this talk, I will present Keldysh quantum field theory for two-dimensional Dirac electrons interacting via instantaneous Coulomb interactions. We will focus on the effect of the dynamical screening of the Coulomb interaction on transport properties of this system. Within the random phase approximation (RPA), we demonstrate that dynamical screening of the Coulomb interaction leads to the emergence of a collective mode, known as plasmon. As the plasmons in 2d are massless, we argue that they constitute a low-energy degree of freedom and should be treated on an equal footing as Dirac fermions. We further derive a coupled system of quantum-kinetic equations for the interacting system of electrons and plasmons. We demonstrate that plasmons show up in thermoelectric transport coefficients as well as in quantities the enter the energy-momentum tensor. I will also discuss possibilities to observe the plasmon contribution in an experiment.