Tuning of longitudinal plasmonic coupling in graphene nanoribbon arrays/sheet hybrid structures at mid-infrared frequencies

Coupling and hybridization of plasmon polaritons can commonly occur in graphene plasmonic nanostructures, providing new possibilities for developing many novel plasmonic optoelectronic devices. Here we have theoretically investigated the longitudinal plasmonic coupling between localized and delocalized surface plasmon polaritons in graphene nanoribbon arrays and monolayer structures in the mid-infrared region. It has been demonstrated that vertical plasmonic coupling can be actively controlled by either the geometric parameters or the Fermi energy in graphene, allowing for strong light–matter interaction. Thanks to the strong plasmon coupling, dual-band perfect absorption with A≈100% and large Rabi splitting exceeding 17.2 meV have been obtained in the absorption spectra of this hybrid system. More intriguingly, we found, by varying the distance between the graphene sheet and the metallic substrate, that periodic spectral nodes can emerge in absorption response of the hybrid mode, which was explained by the mechanism of longitudinal microcavity resonance in this coupled system. The controllable plasmonic coupling and ultrahigh dual-band absorption capability offered by this coupled structure open new avenues for designing tunable multi-channel graphene optoelectronic devices with high performance.