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Tuning emergent magnetism in a Hund's impurity

Nature Nanotechnology volume 10, pages 958–964 (2015)Cite this article

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Abstract

The recently proposed concept of a Hund's metal—a metal in which electron correlations are driven by Hund's rule coupling—can be used to explain the exotic magnetic and electronic behaviour of strongly correlated electron systems of multi-orbital metallic materials. Tuning the abundance of parameters that determine these materials is, however, experimentally challenging. Here, we show that the basic constituent of a Hund's metal—a Hund's impurity—can be realized using a single iron atom adsorbed on a platinum surface, a system that comprises a magnetic moment in the presence of strong charge fluctuations. The magnetic properties can be controlled by using the tip of a scanning tunnelling microscope to change the binding site and degree of hydrogenation of the 3d transition-metal atom. We are able to experimentally explore a regime of four almost degenerate energy scales (Zeeman energy, temperature, Kondo temperature and magnetic anisotropy) and probe the magnetic excitations with the microscope tip. The regime of our Hund's impurity can be tuned from an emergent magnetic moment to a multi-orbital Kondo state, and the system could be used to test predictions of advanced many-body theories for non-Fermi liquids in quantum magnets or unconventional superconductors.

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Figure 1: Electrons in a 3d transition-metal adatom adsorbed to a metallic substrate.
Figure 2: Tuning the magnetism of Fe impurities.
Figure 3: Hund's impurity character of Fe–hydrogen complexes: orbital occupancy and scattering.
Figure 4: Spin excitations of Hund's impurities.
Figure 5: Kondo screening of a Hund's impurity.
Figure 6: Anisotropy and Kondo screening in the six Hund's impurities.

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Acknowledgements

The authors thank H. Brune, F. Donati, M. Ternes and the group of S. Lounis for discussions. A.A.K., T.S., M.S., J.W. and R.W. acknowledge funding from SFB668-A1 and GrK1286 of the Deutsche Forschungsgemeinschaft (DFG). A.A.K. also acknowledges project no. KH324/1–1 from the Emmy-Noether-Program of the DFG. R.W. and J.W. acknowledge funding from European Research Council Advanced Grant ‘ASTONISH’. M.V., T.O.W. and A.I.L. acknowledge support from DFG Research Unit FOR1346. M.V. and A.I.L. also acknowledge computer support NIC, Forschungzentrum Jülich, under project HHH14. A.S. and J.K. acknowledge support from project 15-05872J of the Czech Science Foundation.

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Authors and Affiliations

  1. Department of Physics, Hamburg University, Hamburg, D-20355, Germany

    A. A. Khajetoorians, M. Steinbrecher, T. Schlenk, R. Wiesendanger & J. Wiebe

  2. Institute for Molecules and Materials (IMM), Radboud University, Nijmegen, 6525 AJ, The Netherlands

    A. A. Khajetoorians

  3. Institute of Theoretical Physics, Hamburg University, Hamburg, D-20355, Germany

    M. Valentyuk & A. I. Lichtenstein

  4. Department of Theoretical Physics and Applied Mathematics, Ural Federal University, Ekaterinburg, 620002, Russia

    M. Valentyuk

  5. Institute of Physics, ASCR, Na Slovance 2, Prague, CZ-18221, Czech Republic

    A. Shick & J. Kolorenc

  6. Institute for Theoretical Physics, Bremen Center for Computational Material Science, University of Bremen, Bremen, D-28359, Germany

    T. O. Wehling

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  1. A. A. Khajetoorians
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Contributions

A.A.K., M.S. and T.S. performed the experiments. A.A.K., M.S., T.S. and J.W. analysed the experimental data. M.V., T.O.W. and A.I.L. performed the ab initio and QMC calculations. A.S., J.K., M.V. and T.O.W. performed the ED calculations. A.A.K. and J.W. conceived and designed the experiments. A.A.K., M.V., T.O.W. and J.W. wrote the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to A. A. Khajetoorians.

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Khajetoorians, A., Valentyuk, M., Steinbrecher, M. et al. Tuning emergent magnetism in a Hund's impurity. Nature Nanotech 10, 958–964 (2015). https://doi.org/10.1038/nnano.2015.193

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