Giant photorefractive and photoexpansion effects in a van der Waals semiconductor

Proceedings of the National Academy of Sciences, Volume 123, Issue 13, March 2026. <br/>SignificanceWe report a van der Waals semiconductor, crystalline As2S3, that exhibits an exceptionally large light-induced refractive index change (photorefraction Δnup to 0.3) together with controllable photoexpansion of up to 7%. These effects occur …