In materials science, if you can understand the “texture” of a material—how its internal patterns form and shift—you can begin to design how it behaves. That’s the focus of the work of Zhenglu Li, assistant professor in the Mork Family Department of Chemical Engineering and Materials Science at USC Viterbi School of Engineering. Li’s recently published paper in PNAS, titled “Moiré excitons in generalized Wigner crystals,” demonstrates that the way electrons organize themselves inside a material determines how that material responds to light—and how this organization can be engineered.

“Moiré” is a word that will be familiar to anyone who follows fashion. In the context of textiles, it refers to a larger-scale interference pattern that appears when two repeating patterns are slightly misaligned. Imagine brushing a swatch of velvet in different directions; the material reveals different properties depending on how it is ruffled.

Likewise, in the context of nanoscale materials science, an independent, shimmering or wavelike pattern is formed when two overlapping atomically thin layers are overlaid at an acute angle. The new pattern, moiré superlattice, changes how electrons move, which can give the material unusual properties.