MCW07 Simple Models for Molecular Transport Junctions

By Misha Galperin1, Abraham Nitzan2, Mark A. Ratner1

1. Northwestern University 2. Tel Aviv University

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We review our recent research on role of interactions in molecular transport junctions. We consider simple models within nonequilibrium Green function approach (NEGF) in steady-state regime.

First, we consider electron-electron and electron-phonon interactions within Hubbard-Holstein Hamiltonian. Considerations similar to the equilibrium EOM approach developed by Meir et al.[1] are used on the Keldysh contour to account for the nonequilibrium nature of the junction, and dressing by appropriate Franck-Condon (FC) factors is used to account for vibrational features. Results of the equilibrium EOM scheme by Meir et al. are reproduced in the appropriate limit.

Second, we obtain a unified description of heating in current carrying molecular junctions as well as the electron and phonon contributions to the thermal flux, including their mutual influence. Ways to calculate these contributions, their relative importance and ambiguities in their definitions are discussed. A general expression for the phonon thermal flux is derived and used in a new “measuring technique”, to define and quantify ‘local temperature’ in nonequilibrium systems.

Third, within HOMO-LUMO model we show that light induced current in unbiased junctions can take place when the bridging molecule is characterized by a strong charge-transfer transition. The same model shows current induced light emission under potential bias. We also show that coupling of a molecular bridge to electron-hole excitations in the leads can markedly effect the current. In some cases the contribution from electron-hole excitations can exceed the Landauer elastic current and dominate the observed conduction. Finally, in our latest research we use the HOMO-LUMO model to study Raman scattering of current-carrying molecular junctions.


  1. Phys. Rev. Lett. 66, 3048 (1991); ibid. 70, 2601 (1993)

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  • Misha Galperin; Abraham Nitzan; Mark Ratner (2007), "MCW07 Simple Models for Molecular Transport Junctions,"

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