Dephasing effects in molecular junction conduction: An analytical treatment

A Keldysh nonequilibrium Green's function approach is used in an analytic treatment of transport in oligomeric molecular wire junctions in the presence of dephasing effects. Both the dephasing and molecule-electrode interactions are treated using the self-energy formalism, and limiting analytic forms are obtained for the current as a function of dephasing strength, length, injection energy, molecular hopping integral, and temperature. Dephasing due to the interaction between electrons and thermal phonons is investigated in detail, and we relate the phenomenological dephasing parameter to the inner-sphere reorganization energy. In the single-site limit, we observe transitions in the spectral function from Lorentzian to semicircular as the dephasing strength increases, while for the extended chain we observe both tunneling and hopping behavior. In the limit of strong dephasing, the overall resistance can be expressed as the sum of the contact resistance and a chain-length-dependent hopping term.