Nature Communications 6: Article number: 6136 (2015). Published: 22 January 2015; Updated: 10 February 2015

Moonsub Shim was inadvertently omitted from the list of corresponding authors in this Article. The correct information for correspondence is: ‘Correspondence and requests for materials should be addressed to M.S. mshim@illinois.edu or to L.W.M. lwmartin@berkeley.edu’.