Broad-Band Giant Circular Dichroism in Metamaterials of Twisted Chains of Metallic Nanoparticles

Abstract

By using a discrete-dipole approximation for two-dimensional periodic lattices of scatterers, we show that three-dimensional layer-by-layer metamaterials consisting of twisted arrays of metal-nanoparticle chains exhibit giant circular dichroism spanning over the entire visible regime. The evident broad-band circular dichroism of the metamaterial is not a result of the intrinsic handeness of the constituent meta-atoms as in mainstream chiral designs but arises from the combined action of the anisotropy of each array of chains of nanoparticles, the gradual rotational twist of the metamaterial, and the strong electromagnetic coupling between adjacent layers of nanoparticle chains. As such, it is shown numerically that the degree of circular dichroism of the twisted metamaterial under study depends strongly on the twist angle between two successive lattices of nanoparticle chains and on the degree of anisotropy of each lattice.