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A tunable two-impurity Kondo system in an atomic point contact

Nature Physics volume 7, pages 901–906 (2011)Cite this article

Abstract

Two magnetic atoms, one attached to the tip of a scanning tunnelling microscope and one adsorbed on a metal surface, each constituting a Kondo system, have been proposed as one of the simplest conceivable systems potentially exhibiting quantum critical behaviour. We have succeeded in implementing this concept experimentally for cobalt dimers clamped between a scanning tunnelling microscope tip and a gold surface. Control of the tip–sample distance with subpicometre resolution enables us to tune the interaction between the two cobalt atoms with unprecedented precision. Electronic transport measurements on this two-impurity Kondo system reveal a rich physical scenario, which is governed by a crossover from local Kondo screening to non-local singlet formation due to antiferromagnetic coupling as a function of separation of the cobalt atoms.

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Figure 1: Phase diagram and experimental realization of the two-impurity Kondo problem.
Figure 2: Preparation of the tip Kondo system.
Figure 3: Spectroscopy of the tip Kondo system.
Figure 4: Measurements on two-impurity Kondo system in tunnelling and transport.
Figure 5: Interaction effects between the cobalt atoms.
Figure 6: Schematic phase diagram emerging from the experiment.

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Acknowledgements

We are indebted to I. Affleck for discussion stimulating our research. Further, we acknowledge discussions with M. Fabrizio and D. Jacob. J.B. and L.D. acknowledge support by The Danish Council for Independent Research, Y-h.Z. by the Chinese Scholarship Council, J.K. by the Deutsche Forschungsgemeinschaft through SFB608 and P.W. and K.K. through SFB767. L.B. acknowledges support by the Alexander–von-Humboldt foundation.

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Authors and Affiliations

  1. Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany

    Jakob Bork, Yong-hui Zhang, Peter Wahl & Klaus Kern

  2. Institut for Fysik og Nanoteknologi and Interdisciplinary Nanoscience Center (iNANO), Aalborg Universitet, Skjernvej 4A, DK-9220 Aalborg, Denmark

    Jakob Bork & Lars Diekhöner

  3. Department of Physics, Tsinghua University, Beijing 100084, China

    Yong-hui Zhang

  4. Department of Theoretical Physics, Budapest University of Technology and Economics, H-1111 Budapest, Hungary

    László Borda

  5. Physikalisches Institut, Universität Bonn, Nussallee 12, D-53115 Bonn, Germany

    László Borda & Johann Kroha

  6. Laboratoire de Physique des Solides, Université Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France

    Pascal Simon

  7. Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

    Klaus Kern

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  1. Jakob Bork
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Contributions

J.B. and Y-h.Z. carried out experiments, J.B. analysed the data, L.B. carried out the NRG calculations, P.S. and J.K. provided theoretical support, P.W. carried out the line-shape analysis and J.B., L.D. and P.W. wrote the manuscript. PW, L.D. and K.K. planned and supervised the project. All authors discussed the manuscript.

Corresponding author

Correspondence to Peter Wahl.

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Bork, J., Zhang, Yh., Diekhöner, L. et al. A tunable two-impurity Kondo system in an atomic point contact. Nature Phys 7, 901–906 (2011). https://doi.org/10.1038/nphys2076

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