Electron-electron correlations in molecular tunnel junctions: A diagrammatic approach

Abstract

In this work, the systematic studies of the effect of electron correlations in a bridge of a tunneling junction on transport properties is presented while the leads' electrons are considered to be noninteracting. A diagrammatic technique with respect to the Coulomb interaction is developed for various nonequilibrium bridge Green's functions. Dyson equations on a Keldysh contour for different Keldysh functions is derived. It is shown exactly that the structure of the Dyson equation Keldysh functions of the bridge molecule is the same as for a gas-phase bridge molecule where the zero order nonequilibrium Green's functions are modified by the interaction with the leads' electrons. These Green's functions contain nonvanishing imaginary parts that depend on the interaction between leads' and bridge electrons. As an example, the nonequilibrium bridge Green's functions in the random phase approximation are found where both direct and exchange terms are taken into account.