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., localized states of charge carriers and molecular deformations. At room temperature, incoherent hopping of polarons along the molecule is the dominant mechanism of charge transport. We study the situation far-from-equilibrium where, due to an applied voltage bias, the induced number of charge carriers on the molecule is high and charge correlations become relevant. We develop a diagrammatic theory that accounts in a finite system for all many-particle correlations and their effect on the incoherent transport. We determine the I-V characteristics of short sequences of DNA by expanding the diagrammatic theory up to second order in the hopping parameters. Correlations qualitatively modify the results as compared to those obtained in a mean-field approximation.