Coherent charge transport through molecular wires: Influence of strong Coulomb repulsion

Optically induced transport through semiconductor-based molecular electronics

A tight binding model is used to investigate photoinduced tunneling current through a molecular bridge coupled to two semiconductor electrodes. A quantum master equation is developed within a non-Markovian theory based on second-order perturbation theory with respect to the molecule-semiconductor electrode coupling. The spectral functions are generated using a one dimensional alternating bond model, and the coupling between the molecule and the electrodes is expressed through a corresponding correlation function. Since the molecular bridge orbitals are inside the bandgap between the conduction and valence bands, charge carrier tunneling is inhibited in the dark. Subject to the dipole interaction with the laser field, virtual molecular states are generated via the absorption and emission of photons, and new tunneling channels open. Interesting phenomena arising from memory are noted. Such a phenomenon could serve as a switch.

Compensation of Coulomb blocking and energy transfer in the current voltage characteristic of molecular conduction junctions

We have studied the influence of both exciton effects and Coulomb repulsion on current in molecular nanojunctions. We show that dipolar energy-transfer interactions between the sites in the wire can at high voltage compensate Coulomb blocking for particular relationships between their values. Tuning this relationship may be achieved by using the effect of plasmonic nanostructure on dipolar energy-transfer interactions.

Theoretical and experimental investigations of Coulomb blockade in coupled quantum dot systems

Two strongly coupled quantum dots are theoretically and experimentally investigated. In conductance measurements on a GaAs based low-dimensional system additional features to the Coulomb blockade have been detected at low temperatures. These regions of finite conductivity are compared with theoretical investigations of a strongly coupled quantum dot system and good agreement between the theoretical and the experimental results has been found.

Charge transmission through a molecular wire: The role of terminal sites for the current-voltage behavior

The current-voltage and the conductance-voltage characteristics are analyzed for a particular type of molecular wire embedded between two electrodes. The wire is characterized by internal molecular units where the lowest occupied molecular orbital (LUMO) levels are positioned much above the Fermi energy of the electrodes, as well as above the LUMO levels of the terminal wire units. The latter act as specific intermediate donor and acceptor sites which in turn control the current formation via the superexchange and sequential electron transfer mechanisms. According to the chosen wire structure, intramolecular multiphonon processes may block the superexchange component of the interelectrode current, resulting in a negative differential resistance of the molecular wire. A pronounced current rectification appears if (i) the superexchange component dominates the electron transfer between the terminal sites and if (ii) the multiphonon suppression of distant superexchange charge hopping events between those sites is nonsymmetric.

Negative differential resistance and switching behavior of redox-mediated tunnel contact

Theoretical description of various properties of redox-mediated tunnel contacts is presented. The dependences of the current on the overpotential and bias voltage under the sweeping voltammetry conditions are addressed. The effect of switching between two redox states on the shape of current/voltage characteristics is discussed. The shot noise and telegraph noise of the bridged contacts involving redox group are considered. Functional properties of the contact as a means for the information processing are discussed.