Correction to: Nature Materials https://doi.org/10.1038/nmat3134 published online 24 October 2011.

In the version of this Review Article originally published, parentheses were misplaced and the longitudinal and transverse speeds were inverted in two expressions for Poisson’s ratio in Box 2; the expressions should have read, respectively, ν = (3B/G – 2)/(6B/G + 2) and ν = [½(Vl/Vt)2 − 1]/[(Vl/Vt)2 − 1].