Chiral flatband in refractive index modulated metasurfaces.

Flatband exhibits unique properties, such as slow light effects and a high density of states; incorporating these properties into chiral metasurfaces can significantly enhance chiroptical responses across a range of incident angles. In this study, we establish a theoretical framework to analyze circular dichroism in the presence of broken mirror symmetry along the z-direction. Building on this framework, we employ a theoretical model based on refractive index modulation and partial etching, which lead to a metasurface with a pronounced flatband with chiroptical response. This metasurface holds significant potential for applications in chiral light source emission and detectors, chiral sensing, and enantioseparation, particularly at wide incidence angles.