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We deconvolute the distinct and sometimes competing effects of geometric and material chirality in metastructures created from materials that are intrinsically chiral. We find that overlapping Mie-like resonances in nanodisk arrays leads to 6-fold CD enhancement compared to a uniform film. Furthermore, making the medium chiral does not necessarily increase CD; enhancement depends on the magnitude of the Pasteur parameter and its real and imaginary components. Finally, to demonstrate how geometric and material chirality can be combined, we design a geometrically chiral meta-atom out of chiral media and observe over 9-fold enhancement in both CD andg-factor compared to a metasurface comprised of achiral material. 

Abstract Gyroid optical metamaterials consist of triply periodic chiral networks that are attractive photonic structures due to the combination of intriguing optical properties and spontaneous self‐assembly‐based fabrication routes using materials such as block copolymers. A previous experimental investigation found that gyroid metamaterials support strong circular dichroism, beyond what simulations only considering bulk interactions predict. In this work, simulations are used to unravel the contributions of bulk and surface interactions on the circular dichroism spectra of silver‐infilled gyroid metamaterial films. It is found that surface interactions have a significant, often dominating, contribution to circular dichroism. The relative strength of bulk and surface contributions can be tuned by controlling the crystallographic orientation, termination plane of the film, thickness, metal volume fraction, and defect density. Importantly, the dominance of surface interactions allows double gyroids, which are achiral in the bulk, to support strong circular dichroism responses withg‐factor magnitudes as large as 0.25.