Plasmonics of coupled graphene micro-structures

The optical response of graphene micro-structures, such as micro-ribbons and discs, is dominated by the localized plasmon resonance in the far infrared spectral range. An ensemble of such structures is usually involved and the effect of the coupling between the individual structures is expected to play an important role. In this paper, plasmonic coupling of graphene micro-structures in different configurations is investigated. Whereas a relatively weak coupling between graphene discs on the same plane is observed, the coupling between vertically stacked graphene discs is strong and a drastic increase of the resonance frequency is demonstrated. The plasmons in a more complex structure can be treated as the hybridization of plasmons from more elementary structures. As an example, the plasmon resonances of graphene micro-rings are presented, in conjunction with their response in a magnetic field. Finally, the coupling of the plasmon and the surface polar phonons of SiO2 substrate is demonstrated by the observation of a new hybrid resonance peak around 500 cm−1. (paper)