Nature 523, 576–579 (2015); doi:10.1038/nature14647

The author Elissei Iagodkine was erroneously omitted from the author list of this Letter. They are associated with the affiliation: Dow Chemical Company, 455 Forest Street, Marlborough, Massachusetts 01752, USA, and the Author Contributions section should have included the statement: E.I. provided research-grade BCB used in the preparation of the samples reported, and also participated in helpful discussions. This has been corrected in the online versions of the paper. In addition, authors Haoyu Li and Tom Jackson should have been listed as Haoyo U. Li and Thomas N. Jackson, respectively; the author list, Acknowledgements and Author Contributions sections have therefore been altered accordingly.