Plasmon-Phonon Interaction and Phonon Induced Transparency in Graphene Plasmonic~Nanostructures

Electrons in graphene interact via Coulomb forces but also via an optical phonon-mediated interaction. As a result of the chiral nature of electrons, these two interactions are additive. This phonon-mediated interaction results in strong coupling between the~plasmons~and phonons.~Plasmons~in graphene also interact strongly with the substrate optical phonons. In this talk we will present experimental results on~plasmon-phonon interactions. We patterned disc-shaped~plasmon resonators in CVD grown graphene with radii varying from 16-80 nm and studied plasmon~resonances using IR spectroscopy. Sharp features appear in the~plasmon absorption spectra when the~plasmon~frequencies are close to the phonon frequencies. When the~plasmon~frequency matches the zone-center optical phonon frequency, a narrow transparency dip appears in the~plasmon~absorption spectra. This transparency, which resembles EIT in optics, can be explained in terms of the cancellation between the Coulomb and the phonon-mediated electron-electron interactions. Our theoretical model, based on the eigenvalue equation for confined plasmon~modes, explains the data well and enables us to extract parameters related to the~plasmon-phonon interaction in graphene.