Correction to: Nature Physics, published online 2 December 2019.

In the version of this Perspective originally published, in Fig. 1c the two labels of the vertical axis, ΔuT and ΔuH, were inadvertently swapped; ΔuT should have been at the bottom and ΔuH at the top. All versions of this Perspective have been amended.

© The Author(s), under exclusive license to Springer Nature Limited 2019.