Analysis of circular dichroism in chiral metamaterial at terahertz frequencies

Abstract

Circular dichroism (CD) of chiral metamaterials is of significant interest for bio-sensing and molecular chemistry applications. In this study, using the gammadion shape as an example, the CD effect of gammadion-shaped chiral metamaterials is investigated. We view the gammadion as four Γ-shaped structures. The CD effect of the gammadion is induced by the conductive and magneto-inductive coupling between the weak and strong magnetic fields of the Γ-shaped structures. A large CD effect can be achieved because the magnetic fields excited by the conductive and magneto-inductive coupling show the same and opposing directions for right- and left-handed circular-polarized waves, respectively. This allows analysis of the origin of plasmonic modes in the CD spectrum. We can change the CD effect by changing the conductive and magneto-inductive coupling of the magnetic fields. The CD properties can be tuned by changing either the number of Γ-shaped structures or the layer spacing. These results may guide the design of chiral metamaterials at terahertz frequencies for achieving large CD effects. Furthermore, this approach can be applied to other complex planar structures to gain further insight on the origin of CD modes.