Large Optical Nonlinearity of the Two‐Dimensional Exciton States at a Stacking Fault Interface in BiI3

Abstract

AbstractThe optical Stark effect of an exciton system localized at a stacking fault (stacking fault excitons, SFE) in BiI3 crystals is presented. The SFE states show three very sharp absorption lines called R, S, and T. The excitation laser frequency dependence of the peak shift of the absorption line T is observed in a wide frequency range covering the three SFE states. The peak shift can be seen even for far off‐resonance excitation, and shows drastic change for the on‐resonance excitation of R, S, and T states. This behaviour can be explained by a “dressed exciton” model. The excitation intensity dependence of the peak shift manifests a very large nonlinear optical polarizability of the SFE system.