Correction to: Nature https://doi.org/10.1038/s41586-019-0986-9, published online 6 March 2019.

In the Acknowledgements section of this Letter, the first grant number has been corrected from ‘696656’ to ‘785219’ in the sentence ‘We acknowledge financial support from the European Graphene Flagship Core 2 project under grant agreement 785219…’. The original Letter has been corrected online.