The conductance through a molecular device including electron-electron and electron-phonon interactions is calculated using the numerical renormalization group method. At low temperatures and weak electron-phonon coupling the properties of the conductance can be explained in terms of the standard Kondo model with renormalized parameters. At large electron-phonon coupling a charge analog of the Kondo effect takes place that can be mapped into an anisotropic Kondo model. In this regime the molecule is strongly polarized by a gate voltage which leads to rectification in the current-voltage characteristics of the molecular junction.

The linear transport properties of a model molecular transistor with electron-electron and electron-phonon interactions were investigated analytically and numerically. The model takes into account phonon modulation of the electronic energy levels and of the tunnelling barrier between the molecule and the electrodes. When both effects are present they lead to asymmetries in the dependence of the conductance on gate voltage. The Kondo effect is observed in the presence of electron-phonon interactions. There are important qualitative differences between the cases of weak and strong coupling. In the first case the standard Kondo effect driven by spin fluctuations occurs. In the second case, it is driven by charge fluctuations. The Fermi-liquid relation between the spectral density of the molecule and its charge is altered by electron-phonon interactions. Remarkably, the relation between the zero-temperature conductance and the charge remains unchanged. Therefore, there is perfect transmission in all regimes whenever the average number of electrons in the molecule is an odd integer.Comment: 9 pages, 6 figure

We calculate nonperturbatively the inelastic effects on the conductance through a conjugated molecular-wire -metal heterojunction, including realistic electron-phonon coupling. We show that at subband-gap energies the current is dominated by quantum coherent transport of virtual polarons through the molecule. In this regime, the tunneling current is strongly increased relative to the case of elastic scattering. It is essential to describe the full quantum coherence of the polaron formation and transport in order to obtain correct physics. Our results are generally applicable to one-dimensional atomic or molecular wires. PACS numbers: 85.30.Vw, 73.40.Gk, 73.61.Ph Truly one-dimensional conducting structures, where the confinement lengths for electrons in two directions are of the order of atomic diameters, are currently the subject of much experimental work. Examples include fullerene nanotubes [1], organic molecules bonded to metallic electrodes [2], and dangling-bond (DB) wires created by scanning tunneling microscope lithography of the H-saturated Si(001) surface [3,4]. The conductance properties of such structures are of great importance when one considers their potential as atomic or molecular scale electronic devices. There have been many recent theoretical investigations of electron transport in these systems: for example, Joachim et al. studied Xe atom "wires" [5] and organic molecules [6] using the "elastic scattering quantum chemistry" approach; idealized one-dimensional atomic wires sandwiched between jellium electrodes have been studied using density functional theory [7] and a recursion transfer matrix method [8], while Datta and collaborators studied organic molecules on metal electrodes [9].All the above theoretical work was done within the approximation of elastic transport, where the electronphonon (e-ph) coupling plays no role. But there are good reasons to doubt the validity of this approximation in one-dimensional atomic or molecular scale systems. In small systems, the coupling between electron and other excitations is enhanced. Furthermore, a one-dimensional metal is generally unstable towards a Peierls distortion [10]. Once such a distortion has occurred and produced a band gap, charges added into the system tend to selflocalize and cause distortions of the system which lower the band gap. Such polaronic phenomena have been studied in conducting polymers for decades [11]; electron transport usually proceeds via tunneling into polaron states arising from lattice fluctuations [12].Motivated by this physics and the possibility of measuring the transport through one-dimensional atomic and molecular wires, we report in this Letter the first calculations of the inelastic electronic transport through an atomic-scale wire including realistic e-ph coupling. In our calculations, the quantum coherence of the states is fully retained, i.e., no adiabatic separation between the electronic and phonon degrees of freedom is made. We have chosen to study a conjugated molecular chain as an example since the...

We present a technique to calculate the transport properties through one-dimensional models of molecular wires. The calculations include inelastic electron scattering due to electron-lattice interaction. The coupling between the electron and the lattice is crucial to determine the transport properties in one-dimensional systems subject to Peierls transition since it drives the transition itself. The electron-phonon coupling is treated as a quantum coherent process, in the sense that no random dephasing due to electron-phonon interactions is introduced in the scattering wave functions. We show that charge carrier injection, even in the tunneling regime, induces lattice distortions localized around the tunneling electron. The transport in the molecular wire is due to polaron-like propagation. We show typical examples of the lattice distortions induced by charge injection into the wire. In the tunneling regime, the electron transmission is strongly enhanced in comparison with the case of elastic scattering through the undistorted molecular wire. We also show that although lattice fluctuations modify the electron transmission through the wire, the modifications are qualitatively different from those obtained by the quantum electron-phonon inelastic scattering technique. Our results should hold in principle for other one-dimensional atomic-scale wires subject to Peierls transitions. 85.30.Vw, 73.40.Gk, 73.61.Ph