Circular dichroism in planar nonchiral plasmonic metamaterials

TL;DR

This paper demonstrates theoretically that nonchiral, planar plasmonic metamaterials can exhibit optical activity and circular dichroism due to their lattice symmetry and polarization mode interactions.

Contribution

It reveals that a nonchiral, two-dimensional metallic sphere array can produce circular dichroism through lattice symmetry-induced polarization modes.

Findings

Strong circular dichroism observed around surface plasmon frequencies

Optical activity arises from rectangular lattice symmetry

Chiral triad formation explains dichroism in nonchiral structure

Abstract

It is shown theoretically that a nonchiral, two-dimensional array of metallic spheres exhibits optical activity as manifested in calculations of circular dichroism. The metallic spheres occupy the sites of a rectangular lattice and for off-normal incidence they show a strong circular-dichroism effect around the surface plasmon frequencies. The optical activity is a result of the rectangular symmetry of the lattice which gives rise to different polarizations modes of the crystal along the two orthogonal primitive lattice vectors. These two polarization modes result in a net polar vector, which forms a chiral triad with the wavevector and the vector normal to the plane of spheres. The formation of this chiral triad is responsible for the observed circular dichroism, although the structure itself is intrinsically nonchiral.