Nature Communications 6: Article number: 8948 (2015); Published: 13 November 2015; Updated: 6 June 2016.

This Article contains an error in the penultimate sentence of the penultimate paragraph. This sentence should read: ‘In other words, if one would analyse the minimum current level Imin using a simple parabolic κ(E) WKB approximation, one would extract a much smaller bandgap since Imin is severely underestimated.’