Optical activity in chiral media composed of three-dimensional metallic meta-atoms

We show that the chirality of artificial media, made of a planar periodic arrangement of three-dimensional metallic meta-atoms, can be tailored to cause a strong optical activity. The meta-atoms support localized plasmon polaritons and exhibit a chirality exceeding that of pseudoplanar chiral metamaterials by an order of magnitude. Two design approaches are investigated in detail. The first is the canonical example for a chiral structure, namely a M\"obius strip. The second example is a cut wire-split-ring resonator geometry that can be manufactured with state-of-the-art nanofabrication technologies. Driven into resonance these meta-atoms give rise to a polarization rotation of 30^∘{} per unit cell.