Metasurfaces on Metamaterials: Surface Modes Induce Linear Dichroism in Gyroid Optical Metamaterials*

Optical metamaterials offer the possibility of accessing extraordinary optical properties depending on the arrangement of sub-wavelength structural units. Gyroid-structured optical metamaterials possess a chiral, cubic, and triply-periodic bulk morphology, and exhibit both a circular and linear dichroism, the latter of which is not yet well understood. We have found a strong correlation between the symmetry of the gyroid surface and its polarization-dependent reflectivitiy. Depending on the cutting-plane, the surface terminations break the cubic symmetry of the gyroid, giving rise to the observed dichroism. Our results show that incident light couples into not only localized and propagating plasmonic modes but also nanocavities that form for specific cutting-planes, giving rise to the strong optical anisoptropy. This pronounced surface sensitivity of nanostructured metamaterials has significant consequences for both the design and application of optical metamaterials.