Electron transport in molecular wires mediated via polarons and solitons: Coherent electron-phonon interaction

We consider electron transport through one-dimensional molecular wires connected to two metallic electrodes. The molecules have a substantial band gap (gap between the Highest Occupied Molecular Orbital - HOMO and the Lowest Unoccupied Molecular Orbital LUMO) arising from a Peierls transition due to strong electron-phonon interactions. At small biais, charge carriers can propagate from one electrode to the other by tunneling through the molecule's HOMO-LUMO gap. Owing to the electron-phonon coupling, polarons can be formed in the molecule, even in the tunneling regime. Polaron formation and propagation enhance the transmission through the molecule, especially in the tunneling regime. The presence of a midgap state due to other types of defect in the molecule, such as pre-existing solitons also affects the transport properties. We briefly discuss the effects of polaron-soliton interaction on the transport properties of the wires.