Correction to: Nature Photonics https://doi.org/10.1038/s41566-018-0189-1, published online 18 June 2018.

In the version of this Letter initially published, the identification of light polarization directions (i.e., parallel or perpendicular to the c axis) in optical spectroscopy and ellipsometry results was reversed.

As a result, the directions specified in Fig. 3a,c,d have been corrected. In Fig. 3a,c, from top-down, perpendicular and parallel symbols have now been swapped with each other.

Fig. 3
figure 1

Original and Corrected.

Full size image

In Fig. 3a, from top-down, perpendicular and parallel symbols on the green and orange color keys, respectively, are now swapped with each other (parallel, top, green; perpendicular, orange, bottom). In Fig. 3c from top-down, perpendicular and parallel symbols, respectively, on trace labels are similarly now swapped with each other in both instances. In Fig. 3d, direction of traces are now flipped 180° on the y-axis.

In Fig. 3 caption, in the sentence reading “a,b, Infrared transmission (a) and reflection (b) spectra for incident light polarized perpendicular (dark green) and parallel (orange) to the c axis” the colors “dark green” and “orange” should be swapped to now read: “a,b, Infrared transmission (a) and reflection (b) spectra for incident light polarized perpendicular (orange) and parallel (dark green) to the c axis”

Additionally, discussion of perpendicular and parallel directions in paragraph 6, third and fourth sentences, respectively, were corrected as follows:

“When the polarization was parallel to the c axis, the absorption edge was observed at 4.5 μm (0.27 eV). However, when the polarization was perpendicular to the c axis, the absorption edge was blueshifted to 1.6 μ m (0.76 eV).”

The original Letter has been corrected online.