Coherent transport, single-electron tunneling and switching in π-conjugated molecular junctions

Prof. Dr. Klaus Richter, Universität Regensburg [Homepage]

Prof. Dr. Milena Grifoni, Universität Regensburg [Homepage]

Aim of the project is the investigation of non-equilibrium charge transport across conjugated π-systems,
with focus on the interplay between molecular conformation and strong Coulomb
interactions, yielding Coulomb and vibron blockade, memory and switching effects. The
experimental setups to be mimicked are either transport in a three-terminal configuration
where the molecular bridge can act as a single-electron transistor, or STM experiments.
The molecules we have in mind are predominantly biphenyl- and terphenyl-based complexes
(where the torsional degrees of freedom between the different phenyl rings can have a large
influence on charge transport), as well as other oligophenyls. For example, in biphenyl and
terphenyl the angular dependence of the adiabatic potential surfaces is different for the neutral
and charged molecular configuration. This implies e.g. that, depending on the charge on
the molecule, there is a regime of strong and weak inter-phenyl coupling.
Following the scope of the preceeding proposal, and in order to tackle the different situations
(static and vibronic properties; coherent transport and single-electron tunneling) various complementary
methods will be employed and further developped. On the one side, microscopic
interacting Hamiltonians will be devised based on a tight-binding description of the atomic
orbitals. The transport problem will then be solved either within a generalized master equation
approach for the reduced density matrix including coherences, or with non-equilibrium
Green function techniques based either on the Keldysh Green function formalism or on the
equation of motion method. On the other side, complementary to these model-based and
semi-quantitative descriptions, we plan to further persue numerical DFT-based and quantum
chemistry calculations, in cooperation with other groups of the priority program.