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Observation of quantum interference in molecular charge transport

Abstract

As the dimensions of a conductor approach the nanoscale, quantum effects begin to dominate, and it becomes possible to control the conductance through direct manipulation of the electron wavefunction. Such control has been demonstrated in various mesoscopic devices at cryogenic temperatures1,2,3,4, but it has proved to be difficult to exert control over the wavefunction at higher temperatures. Molecules have typical energy level spacings (eV) that are much larger than the thermal energy at 300 K (25 meV), and are therefore natural candidates for such experiments. Previously, phenomena such as giant magnetoresistance5, Kondo effects6 and conductance switching7,8,9,10,11 have been observed in single molecules, and theorists have predicted that it should also be possible to observe quantum interference in molecular conductors12,13,14,15,16,17,18, but until now all the evidence for such behaviour has been indirect. Here, we report the observation of destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. We studied five different rigid π-conjugated molecular wires, all of which form self-assembled monolayers on a gold surface, and find that the degree of interference can be controlled by simple chemical modifications of the molecular wire.

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Figure 1: Conductance measurements on molecular wires.
Figure 2: Origin of interference in cross-conjugated molecules.
Figure 3: Two-dimensional conductance histograms.
Figure 4: Calculated dI/d V curves for AQ-MT and OPE3-MT.

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Acknowledgements

The authors thank T. Oosterkamp and F. Galli for making their equipment and expertise available, J. van Ruitenbeek and M. Trouwborst for discussions and D. Myles for his initial synthetic efforts. This study was financed by a VIDI grant (to S.J.vdM.) from the Netherlands Organization for Scientific Research (NWO), by the Dutch Ministry of Economic Affairs via NanoNed (to H.V., project GMM.6973), by the FTP (grant no. 11-104592 to T.M.) and The Sapere Aude program under the Danish Council for Independent Research (grant no. 11-105139 to K.S.T.).

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C.M.G., H.V. and S.J.vdM. performed AFM measurements and carried out data analysis. H.V. and J.C.H. designed and synthesized the molecules, and made and characterized the SAMs. T.M. and K.S.T. performed the calculations. C.M.G., H.V., J.C.H. and S.J.vdM. designed the experiment. All authors discussed the results and commented on the manuscript.

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Correspondence to Sense Jan van der Molen.

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Guédon, C., Valkenier, H., Markussen, T. et al. Observation of quantum interference in molecular charge transport. Nature Nanotech 7, 305–309 (2012). https://doi.org/10.1038/nnano.2012.37

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