Artistic view of the established contact of a molecule bridging a gold nano-bridge with induced superconductivity.

The properties of molecular transport can be analyzed by measuring the conductance or its derivative, giving first insights to molecular levels and coupling to the electrodes.[1] Furthermore, excitations of the molecule can be found by inspecting the inelastic electron tunneling spectrum (IETS) via the d²I/dV² signal.[2]
However, the possible composition of several conduction channels of electronic transport in a metal-molecule-metal junction has not been explored in much detail yet. With the help of shot noise measurements, it has been shown that Pt-H2-Pt junctions with a conductance of 1 G0 accommodate indeed a single perfectly transmitted channel.[3]


Two measured Pb single atom contacts with fits, both exhibiting sets of three transmission channels but with different transmission probability: [0.99,0.38,0.38] and [0.52,0.29,0.20]

The aim of this project is to analyze the transport properties of a molecular junction with respect to the number and transmission of channels. For this purpose a superconducting MCBJ design is combined with highly conductive molecules like 1,4-benzendithiol. If a contact through the molecule is established, an I-V spectrum will reveal the composition of channels via multiple Andreev reflections (MAR).[4] This can only be done at very low temperatures well below the critical temperature TC. For this purpose, a 1K stick was equipped with break junction mechanics and high frequency filters to reach high energy resolution for MAR spectra in Pb-MCBJ.
First results obtained for single atom Pb contacts can be seen in Figure 1, where two different contacts have been analyzed via MAR spectroscopy to distinguish their channel composition. They contacts both show a similar conductance, but the transmission channel composition clearly differs.


Publications

D. Weber and E. Scheer, Superconducting properties of lithographic lead break junctions, Nanotechnology  (2018). URL: http://iopscience.iop.org/article/10.1088/1361-6528/aa99b8

  1. L. Zotti, Th. Kirchner, J.-C. Cuevas, F. Pauly, Th. Huhn, E. Scheer, A. Erbe, Small 6, 1529–1535 (2010)
  2. J. C. Cuevas, E. Scheer, World Scientific, Molecular Electronics: An Introduction to Theory and Experiment 2nd Edition (2017)
  3. R. H. M. Smit, Y. Noat, C. Untiedt, N. D. Lang, M. C. van Hemert, J. M. van Ruitenbeek, Nature 419, 906-909 (2002)
  4. E. Scheer, P. Joyez, D. Esteve, C. Urbina, M. H. Devoret, Phys. Rev. Lett. 18, 3535 (1997)
  5. J. C. Cuevas, A. Martin-Rodero, A. Levy Yeyati, Phys. Rev. B 54, 7366 (1996)

Information

Contributors: D. Weber
Former Contributors: A. Nyáry
External cooperations: T. Huhn (Uni KN), C. Cuevas (Universidad Autónoma de Madrid)
Fundings: SFB 767 project C2
Period: 2013-now