Chiral Bismuth Halide Crystals: Polarizability-Driven Birefringence and Wave Plate Functionality

Birefringent crystals, essential for modulating light polarization, are indispensable in advanced optical applications, including polarizing microscopes, optical isolators, and wave plates. Yet, many prevalent commercial options suffer from design complexities due to their multilayered architectures. Here, we report a 0D chiral bismuth halide perovskite with in-plane anisotropy that enables efficient birefringence and practical application in achromatic quarter-wave plates (QWPs). Remarkably, we demonstrate that chirality-induced structural polarizability strongly amplifies anisotropic light–matter interactions, enhancing birefringence by more than 5-fold compared with the racemic analogue. Furthermore, the birefringent crystal functions as a QWP with broadband achromatic retardation spanning from 510 to 800 nm. This work introduces a novel structural polarizability engineering strategy for significantly boosting birefringence and advancing wave plate technologies.