Design of in-plane graphene metasurfaces for generating strong mid-infrared circular dichroism

We show that graphene plasmonic metasurfaces can create strong circular dichroism (CD) in mid-infrared due to the nanostructure's geometrical chirality and the plasmonic coupling between the elements in a chiral unit. This is best demonstrated by the plasmonic CD yielded by graphene nanodisks aligned along a 3D helical line [1]. In contrast with the 3D nanodisks assemblies, which pose fabrication difficulty, in-plane graphene nanostructures are more favorable for the plasmonic CD generation. The interaction between the in-plane graphene nanoscale elements can be enhanced by placing them above a graphene sheet. In this way, the in-plane chiral structures (metasurfaces) can exhibit comparable differential absorption of the left and right circular polarizations of light to that of the graphene nanodisks assemblies. The strong plasmonic CD generated by the graphene nanostructures and metasurfaces provides us a possibility to enhance the vibrational optical activity of important biomolecules, such as DNA and peptides, whose vibrational modes overlap well with the frequency interval of graphene plasmons.

[1] Kong X.-T., Zhao R., Wang Z. & Govorov A. O. Nano Lett. 2017, 17, 5099