Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 44: Transport: Nanoelectronics III - Molecular Electronics 2

TT 44.2: Talk

Thursday, March 29, 2012, 15:15–15:30, BH 334

Thermopower of biphenyl-based single-molecule junctions — •Marius Bürkle¹, Linda A. Zotti², Janne K. Viljas³, Thomas Wandlowski⁴, Marcel Mayor⁵, Gerd Schön¹, and Fabian Pauly¹ — ¹Institut für Theoretische Festkörperphysik and DFG Center for Functional Nanostructures, Karlsruhe Institute of Technology, Karlsruhe, Germany — ²Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain — ³Low Temperature Laboratory, Aalto University, Aalto, Finland — ⁴Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland — ⁵Department of Chemistry, University of Basel, Basel, Switzerland

Employing ab initio electronic structure calculations combined with non-equilibrium Green’s function techniques we study the dependence of the thermopower on the degree of π-conjugation in biphenyl-based single molecule gold junctions. We control the degree of π-conjugation by changing the torsion angle ϕ between the two phenyl rings by means of alkyl side chains connected to the molecules. We find that the absolute value of the thermopower decreases weakly as cos²ϕ. We show that the observed cos²ϕ dependence is robust with respect to different anchoring groups and binding positions. The anchoring group determines the sign of the thermopower. Sulfur and amine give rise to Q>0 and cyano to Q<0 respectively. Different binding positions on the contrary lead to variations of the absolute values of the thermopower. The observed ab initio results are found to be described well by means of a π-electron tight binding model.