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X. Zhao, G. Kastlunger, R. Stadler:
"Quantum interference effects in coherent electron transport through single molecule junctions with branches containing ferrocene";
Poster: Workshop "Many paths to interference: a journey between quantum dots and single molecule junctions", Max Planck Institute for the Physics of Complex Systems, Dresden, Germany; 18.04.2017 - 20.04.2017.

Quantum interference (QI) effects have received a lot of recent attention as a potential enabling tool for the implementation of logic gates or data storage in single molecule junctions. In this context branched molecules are of particular interest because they can cause either constructive or destructive QI in the electron transport through the junction depending on whether the two branches are symmetry equivalent or this symmetry is disturbed by structural variations or local charging. In our theoretical study where we combine a nonequilibrium Green¢s function (NEGF) approach with density functional theory (DFT) we investigate branched compounds containing ferrocene moieties in both branches which due to their metal centers are designed to allow for such asymmetry induced by local charging. In these compounds the ferroecene moieties are connected to pyridil anchor groups either directly or via acetylene spacers in a meta-connection where we also compare our results with those obtained for the respective single-branched molecules with both meta- and para-connections between the metal center and the anchors. We find two destructive QI features, one slightly above the highest occupied (HOMO) and one slightly below the lowest unoccupied molecular orbital (LUMO), even for the uncharged branched compound with spacer groups inserted. In principle these features can result from a variety of structural aspects of this molecule, namely i) the two paths provided by the two branches, ii) the existence of several nearly degenerate states on the ferrocene and iii) the meta-connections between the anchor groups and the redox-active moiety. In an analysis based on a decomposition of MOs into fragment orbitals (FOs) which we focus on the QI feature near the LUMO because it dominates the conductance, we find the meta-connections to be its main cause and the presence of the acetylene spacers also a necessary requirement while local charging on one of the branches does not have a significant influence on the conductance.

Molecular electronics, conductance of molecular nanojunctions, electrochemical properties, quantum interference effects

Projektleitung Robert Stadler:
Elektrochemische Interferenz