Far-Field Excitation of Acoustic Graphene Plasmons with a Metamaterial Absorber

When a graphene sheet is placed near a metal surface, it supports a special type of highly confined and low-loss electromagnetic mode called acoustic graphene plasmons (AGPs). AGPs squeeze infrared photons into extremely confined areas down to a subnanometric scale and provides a unique platform for strong light-matter interactions. However, the efficient excitation of AGPs is a challenge due to the large momentum mismatch between free-space light and AGPs. With theoretical analysis and numerical simulations, it is shown that the far-field excitation of AGPs is realized by integrating graphene in a metal-insulator-metal (MIM) metamaterial with magnetic resonance (MR). More than ten graphene plasmonic modes are excited in the midinfrared range, resulting in a multiresonant spectra with Fano-like characteristics at each resonant wavelength. The proposal opens a new door to explore the strong plasmonic coupling between graphene and metallic metamaterials down to atomic scale for extreme nanophotonics. The potential applications range from ultracompact tunable metamaterials and ultrasensitive infrared spectroscopy to single-molecule optics, quantum plasmonics, and others.