A tri-helical model for nanoplasmonic gyroid metamaterials

Metallic gyroid metamaterials are formed by a combination of nanoplasmonic helices leading to unique and complex optical characteristics. To unravel this inherent complexity we set up an analytic tri-helical metamaterial model that reveals the underlying physical properties. This analytic tri-helical model is complete in the sense that it is only dependent on the structure's geometric and material parameters. It allows us to elucidate the characteristic transverse and longitudinal modes of the metal nano-gyroid as well as explain the surprisingly small optical chirality of gyroid metamaterials that is observed in experiments. We argue that this behaviour originates from the interconnection of multiple helices of opposing handedness.