Nature Reviews Physics (2020) https://doi.org/10.1038/s42254-020-0210-8 Published online 05 August 2020

In the original version of this manuscript, the graph in Fig 1a was incorrectly rendered, and two traces were not clearly visible. Panels c and d in Fig 3 were mislabelled in the caption and in the text. A reference in the caption of Fig 6 linked to the wrong citation. Finally, in the list of highlighted references, the text referred to a singular ‘surface state’ instead of the plural ‘surface states’, which is more accurate. These have been corrected in the HTML and PDF versions of the manuscript.