Dresden 2014 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 72: Transport: Molecular Electronics II
TT 72.1: Talk
Wednesday, April 2, 2014, 15:00–15:15, HSZ 304
Conductance and thermopower of long molecular wires — •F. Rochau1, M. Kotiuga2,3, T. J. Hellmuth4, J. B. Neaton2,3, and F. Pauly1 — 1Department of Physics, University of Konstanz, Germany — 2Molecular Foundry, Lawrence Berkeley National Laboratory, California, USA — 3Department of Physics, University of California, Berkeley, USA — 4Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, Germany
We study the transition from coherent tunneling to incoherent hopping for the conductance G and the thermopower S of long molecular wires [1]. Using a tight-binding model for the electronic structure combined with Green’s function techniques to describe transport, we include dephasing by means of Büttiker probes. We discuss the one-dimensional chain as well as several benzene-based molecular junctions (oligophenylenes, polyacenes and polyphenanthrenes). For the one-dimensional chain we derive analytical formulas for the length dependence of the phase-coherent G and S, distinguishing off-resonant, band-edge, and on-resonant transport. Irrespective of the regime and the system considered, we find an ohmic inverse length dependence of G and a saturating S for long molecular wires, when dephasing is included. The power factor S2G of long wires is therefore determined by G. Finally, we study the huge thermopower resulting from transmission nodes for the polyphenanthrenes and observe how they disappear when decoherence is added.
F. Rochau, M. Kotiuga, T. Hellmuth, J. B. Neaton, and F. Pauly, in preparation