Charge correlations in polaron hopping through molecules

In many organic molecules the strong coupling of excess charges to vibrational modes leads to the formation of polarons, i.e., a localized state of a charge carrier and a molecular deformation. Incoherent hopping of polarons along the molecule is the dominant mechanism of transport at room temperature. We study the far-from-equilibrium situation where, due to the applied bias, the induced number of charge carriers on the molecule is high enough such that charge correlations become relevant. We develop a diagrammatic theory that exactly accounts for all many-particle correlations functions for incoherent transport through a finite system. We compute the transport properties of short sequences of DNA by expanding the diagrammatic theory up to second order in the hopping parameters. The correlations qualitatively modify the I-V characteristics as compared to those approaches where correlations are dealt with in a mean-field type approximation only.