Correction to: Nature Physics https://doi.org/10.1038/s41567-018-0401-8, published online 21 January 2019.

The authors wish to add the following sentence in the Acknowledgements: “The authors are grateful to S. Kivelson, B. Fine, K. M. Shen and D. Hawthorn for insightful discussions.” The online versions of this Letter have been amended accordingly.