Correction to: Nature Physics https://doi.org/10.1038/s41567-018-0064-5, published online 2 March 2018.

In the version of this Review Article originally published, three of the citations corresponded to the wrong references. Ref. 16 should have corresponded to Nature 533, 513–516 (2016), ref. 17 to Nat. Mater. 16, 94–100 (2016), and ref. 18 to Phys. Rev. Appl. 6, 054001 (2016).

In addition, in Fig. 1e, the thin black data line should have been a continuation of the thick blue one; the credit citations for panels b and c of Fig. 5 were the wrong way around; they should have been to ref. 96 for b and ref. 93 for c; and references 108, 109 and 110 were appearing out of order, though correctly cited.

These errors have been corrected in the online version of the Review Article.