Correction to: Nature Reviews Materials https://doi.org/10.1038/s41578-019-0133-0, published online 26 September 2019

In the version of this article initially published, there was an error in the plotting of Au119 in Fig. 2; a corrected image is shown as Fig. 1 below.

Fig. 1: Updated Fig. 2.
figure 1

The value of the imaginary permittivity ε is plotted at the crossover wavelength (λco) at which the real permittivity is zero. Materials with an imaginary permittivity smaller than 2 at the crossover wavelength exhibit near-zero-index (NZI) properties. The lines connect the different measured values of Im{ε} for a given statically tunable material and illustrate their variability. ENZ, ε-near-zero; hBN, hexagonal boron nitride.