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TT: Fachverband Tiefe Temperaturen

TT 44: Transport: Nanoelectronics III - Molecular Electronics 2

TT 44.8: Vortrag

Donnerstag, 29. März 2012, 17:00–17:15, BH 334

STM transport theory for π-conjugated molecules on thin insulating films — •Sandra Sobczyk, Andrea Donarini, and Milena Grifoni — Institute of Theoretical Physics, University of Regensburg, Germany

In seminal experiments, scanning tunneling microscopy (STM) has been performed on molecules on insulating films having a thickness of only few atomic layers. The layer is in turn grown on top of a metallic surface. At the same time the electrons can still tunnel through the insulating films, facilitating spectroscopy and imaging with low-temperature STM.

We present an STM theory that is sufficiently general to be applied to any STM device consisting of a π-conjugated molecule weakly coupled to the substrate and the tip. We show that the strongly asymmetric coupling to the leads, that is provided by the geometry of the substrate and the tip, leads to qualitatively different, energy dependent transfer rates. We apply the theory to a benzene molecule and we demonstrate that the mentioned differences in the rates yield two different types of current suppression, one caused by Coulomb interaction and one by interference effects due to involved orbitally degenerate states. We also simulate constant height current maps and identify the characteristic topographic fingerprints of the two forementioned blocking mechanisms.