Article

Charge-memory polaron effect in molecular junctions

Physical review. B, Condensed matter (Impact Factor: 3.77). 02/2008; DOI: 10.1103/PhysRevB.78.085409
Source: arXiv

ABSTRACT The charge-memory effect, bistability and switching between charged and neutral states of a molecular junction, as observed in recent STM experiments, is considered within a minimal polaron model. We show that in the case of strong electron-vibron interaction the rate of spontaneous quantum switching between charged and neutral states is exponentially suppressed at zero bias voltage but can be tuned through a wide range of finite switching timescales upon changing the bias. We further find that, while junctions with symmetric voltage drop give rise to random switching at finite bias, asymmetric junctions exhibit hysteretic behavior enabling controlled switching. Lifetimes and charge-voltage curves are calculated by the master equation method for weak coupling to the leads and at stronger coupling by the equation-of-motion method for nonequilibrium Green functions. Comment: 4 pages, 5 figures, submitted

0 Bookmarks
 · 
104 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Currently, molecular tunnel junctions are recognized as important active elements of various nanodevices. This gives a strong motivation to study physical mechanisms controlling electron transport through molecules. Electron motion through a molecular bridge is always somewhat affected by the environment, and the interactions with the invironment could change the energy of the traveling electron. Under certain conditions these inelastic effects may significantly modify electron transport characteristics. In the present work we describe inelastic and dissipative effects in the electron transport occurring due to the molecular bridge vibrations and stochastic thermally activated ion motions. We intentionally use simple models and computational techniques to keep a reader focused on the physics of inelastic electron transport in molecular tunnel junctions. We consider electron-vibron interactions and their manifestations in the inelastic tunneling spectra, polaronic effects and dissipative electron transport. Also, we briefly discuss long-range electron transfer reactions in macromolecules and their relation to the electron transport through molecular junctions.
    Physics Reports 01/2013; 509(1). · 22.93 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent advances in synthesis and electrical characterization of nanofibers and nanotubes made out of various conjugated polymers attract attention of the research community to studies of transport properties of these materials. In this work we present a theoretical analysis of electron transport in polymer nanofibers assuming them to be in conducting state. We treat a conducting polymer as a network of metallic-like grains embedded in poorly conducting environment, which consists of randomly distributed polymeric chains. We analyze the contribution from intergrain electron resonance tunneling via intermediate states localized on the polymeric chains between the grains. Correspondingly, we apply the quantum theory of conduction in mesoscopic systems to analyze this transport mechanism. We show that the contribution of resonance electron tunneling to the intergrain electron transport may be predominating, as follows from experiments on the electrical characterization of single polyaniline nanofibers. We study the effect of temperature on the transport characteristics. We represent the thermal environment as a phonon bath coupled to the intermediate state, which provides electron tunneling between the metallic-like grains. Using the Buttiker model within the scattering matrix formalism combined with the nonequilibrium Green's functions technique, we show that temperature dependencies of both current and conductance associated with the intergrain electron tunneling, differ from those typical for other conduction mechanisms in conducting polymers. Also, we demonstrate that under certain conditions the phonon bath may cause suppression of the original intermediate state accompanied by emergence of new states for electron tunneling. The temperature dependencies of the magnitudes of the peaks in the transmission corresponding to these new states are analyzed.
    01/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We develop a computational method for evaluating the damping of vibrational modes in monatomic metallic chains suspended between bulk crystals under external strain. The damping is due to the coupling between the chain and contact modes and the phonons in the bulk substrates. The geometry of the atoms forming the contact is taken into account. The dynamical matrix is computed with density-functional theory in the atomic chain and the contacts using finite atomic displacements while an empirical method is employed for the bulk substrate. As a specific example, we present results for the experimentally realized case of gold chains in two different crystallographic directions. The range of the computed damping rates confirms the estimates obtained by fits to experimental data [ T. Frederiksen et al. Phys. Rev. B 75 205413 (2007)]. Our method indicates that an order-of-magnitude variation in the harmonic damping is possible even for relatively small changes in the strain. Such detailed insight is necessary for a quantitative analysis of damping in metallic atomic chains and in explaining the rich phenomenology seen in the experiments.
    Phys. Rev. B. 01/2009; 80(4).

Full-text (2 Sources)

Download
51 Downloads
Available from
May 29, 2014