Surface Structure Dependent Circular Dichroism in Single and Double Gyroid Metamaterials

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 with g-factor magnitudes as large as 0.25.