Symmetric Meta-Absorber-Induced Superchirality

Chiral light-matter interaction in plasmonic metamaterials represents a new paradigm in optics. However, most previously reported works require structural chirality based on asymmetric three-dimensional architectures, imposing a significant cost barrier in scalable manufacturing. Here, the generation of superchiral light-matter interaction in symmetric metal-dielectric-metal (MDM) metamaterial structures is theoretically proposed. Due to the interplay of the spatially separated and enhanced electric (E-) and magnetic (H-) fields with complementary profiles, a superchiral localized hotspot can be generated in MDM structures when an appropriate phase condition is satisfied. By introducing chiral molecules into the spacer layer, the circular dichroism (CD) signal of the coupled system can be enhanced significantly. The origin of the enhanced CD is attributed to the inherent and induced CD signals of the coupled system, which are derived from the direct molecular CD response and the asymmetric absorption of circularly polarized light by the metallic nanostructure. It is demonstrated that the metamaterial-induced CD response contributes dominantly to the overall CD response of the coupled system, and a 1300-fold enhancement factor can be obtained when on-resonance chiral molecules are adsorbed in the optical superchiral field in the spacer layer. This finding paves the way toward the development of practical and scalable platforms for new chiroptical applications.