•Axel Thielmann¹, Matthias H. Hettler¹, Jürgen König² und Gerd Schön^1,3
1Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76021 Karlsruhe, Germany
²Institut für Theoretische Physik III, Ruhr-Universität Bochum, 44780 Bochum, Germany
³Institut für Theoretische Festkörperphysik , Universtität Karlsruhe, 76128 Karlsruhe, Germany

We consider charge transport through single molecules coupled weakly to metal electrodes via tunneling barriers. The molecule is represented by the Anderson impurity model which is the simplest model that includes Coulomb interactions U. We calculate the current and current noise within a first-order perturbation expansion in the coupling strength using a diagrammatic technique. Analytical results for current, noise and the Fano factor, F,(depending on the ratio of the couplings to the left and right electrodes) are presented and discussed for all transport regimes involving a single interacting (molecular) level (Phys. Rev. B 68, 115105 (2003)). Furthermore an extended model with two levels will be considered, where the effects of asymmetric coupling and photon-relaxation can be studied. Negative differential conductance (NDC) behavior leading to super-poissonian noise (F > 1) can be observed in the case of asymmetric coupling to the leads and is distroyed by strong relaxation rates. In addition to the numerical evaluation analytical expressions for several transport regimes will be presented.