reSeArCH Letter
Author contributions K.I. and H.I. conceived the idea and directed the project.
Y.Y., K. Matsushima and H.I. conducted the experiments and theoretical
calculations. K. Matsui, A.T. and N.M. conducted the STM experiments.
F.W. conducted the AFM experiments. Y.M. supervised the scanning probe
microscopy experiments and provided advice on spectroscopic analysis. H.I.
and K.I. prepared the manuscript with feedback from the other authors.
Competing interests The authors declare no competing interests.
Additional information
Extended data is available for this paper at https://doi.org/10.1038/s41586-
019-1331-z.
Supplementary information is available for this paper at https://doi.org/
10.1038/s41586-019-1331-z.
Reprints and permissions information is available at http://www.nature.com/
reprints.
Correspondence and requests for materials should be addressed to H.I. or K.I.
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claims in published maps and institutional affiliations.© The Author(s), under exclusive licence to Springer Nature Limited 2019392 | NAtUre | VOL 571 | 18 JULY 2019