Giant and dynamically tunable plasmonic circular dichroism in graphene ribbons and Z-shaped metal metamaterials

Abstract

Plasmonic chirality has drawn a lot of attention owing to its strong and tunable circular dichroism (CD) effects and its desirable applications in bio-sensing, chiral molecules analysis, etc. In this work, the CD response in the mid-infrared region of a metamaterial consisting of Z-shaped metal array and graphene ribbons has been studied theoretically. Benefiting from symmetry breaking and electromagnetic coupling effect, the strong CD signal is generated by the metamaterial and the maximum CD value could reach 22%, which is much larger than that of reported graphene-based chiral systems. In particular, the intensity and peak position of the CD response could be dynamically controlled by the Fermi level in a large range. Meanwhile, the CD response also could be actively controlled by changing the number and the width of graphene ribbons, the distance between the graphene ribbons and Z-shaped metal array, and so on. Furthermore, the CD effect is sensitive to the ambient medium. Therefore, the graphene ribbons and metal metamaterial could be potentially utilized in bio-sensing and related fields.