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Evidence for spinarons in Co adatoms

Nature Physics volume 20, pages 28–33 (2024)Cite this article

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Abstract

Cobalt atoms on the (111) surfaces of noble metals are considered to be prototypical systems for the Kondo effect in scanning tunnelling microscopy experiments. Recent first-principles calculations, however, suggest that the experimentally observed spectroscopic zero-bias anomaly can be interpreted in terms of excitations of the spin of the Co atom and the formation of a novel many-body state, namely, the spinaron, rather than from a Kondo resonance. The spinaron is a magnetic polaron that results from the interaction of spin excitations with conduction electrons. However, the experimental confirmation for the existence of spinarons remains elusive. Here we present experimental evidence for spinaronic states in Co atoms on the Cu(111) surface. Our spin-averaged and spin-polarized scanning tunnelling spectroscopy measurements in high magnetic fields allow us to discriminate between the different existing theoretical models and to invalidate the prevailing Kondo-based interpretation of the zero-bias anomaly. Our extended ab initio calculations instead suggest the presence of multiple spinaronic states. Thus, our work provides the foundation to explore the characteristics and consequences of these intriguing hybrid many-body states as well as their design in artificial nanostructures.

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Fig. 1: Schematic of the field-induced splitting of magnetic resonances and excitations.
Fig. 2: Magnetic-field-dependent splitting of the ZBA.
Fig. 3: Implementation and results of spin-resolved measurements on Co/Cu(111).
Fig. 4: Orbital-resolved LDOS and theoretical inelastic tunnelling spectra.

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Data availability

The data supporting the findings of this study are available from the corresponding authors upon request. Source data are provided with this paper.

Code availability

The computer code used for data analysis is available from the corresponding authors upon request.

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Acknowledgements

This research was supported by the DFG through SFB 1170 ‘ToCoTronics’ and the Würzburg-Dresden Cluster of Excellence ct.qmat, EXC2147, via project ID 390858490. M.B., A.O. and F.F. thank P. Sessi (Max-Planck-Institut für Mikrostrukturphysik, Halle, Germany) for bringing this scientific topic to our attention. J.B. acknowledges support by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant no. 856538, project ‘3D MAGiC’). S.L. acknowledges S. Brinker and A. Weismann for fruitful discussions.

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Authors and Affiliations

  1. Physikalisches Institut, Experimentelle Physik II, Julius-Maximilians-Universität Würzburg and Würzburg-Dresden Cluster of Excellence ct.qmat, Würzburg, Germany

    Felix Friedrich, Artem Odobesko & Matthias Bode

  2. Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, Jülich, Germany

    Juba Bouaziz & Samir Lounis

  3. Faculty of Physics, University of Duisburg-Essen and CENIDE, Duisburg, Germany

    Samir Lounis

  4. Wilhelm Conrad Röntgen-Center for Complex Material Systems (RCCM), Julius-Maximilians-Universität Würzburg, Würzburg, Germany

    Matthias Bode

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Contributions

F.F., A.O., M.B. and S.L. conceived the experiments. F.F. and A.O. conducted the measurements and analysed the data. J.B. performed the first-principles simulations. S.L. and M.B. supervised the project. All authors discussed the results. F.F. and S.L. wrote the manuscript with input from all authors.

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Correspondence to Artem Odobesko or Samir Lounis.

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Nature Physics thanks Jörg Kröger and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–7 and discussion.

Source data

Source Data Fig. 1

Data points used for the schematic of the field-induced splitting of magnetic resonances and excitations.

Source Data Fig. 2a

STM data of the Cu(111) surface with single adsorbed Co atoms (Fig. 2a).

Source Data Fig. 2

Unprocessed experimental data of magnetic-field-dependent splitting of the ZBA (Fig. 2b–h).

Source Data Fig. 3a

STM data of the Cu(111) surface decorated with Fe islands, Nc molecules and Co atoms.

Source Data Fig. 3

Unprocessed experimental data and fits of spin-resolved measurements on Co/Cu(111).

Source Data Fig. 4

Calculated orbital-resolved LDOS and theoretical inelastic tunnelling spectra.

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Friedrich, F., Odobesko, A., Bouaziz, J. et al. Evidence for spinarons in Co adatoms. Nat. Phys. 20, 28–33 (2024). https://doi.org/10.1038/s41567-023-02262-6

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