Electrothermal Control of Graphene Plasmon-Phonon Polaritons

Graphene plasmons are known to offer an unprecedented level of confinement and enhancement of electromagnetic field. They are hence amenable to interacting strongly with various other excitations (for example, phonons) in their surroundings and are an ideal platform to study the properties of hybrid optical modes. Conversely, the thermally induced motion of particles and quasiparticles can in turn interact with electronic degrees of freedom in graphene, including the collective plasmon modes via the Coulomb interaction, which opens up new pathways to manipulate and control the behavior of these modes. This study demonstrates tunable electrothermal control of coupling between graphene mid-infrared (mid-IR) plasmons and IR active optical phonons in silicon nitride. This study utilizes graphene nanoribbons functioning as both localized plasmonic resonators and local Joule heaters upon application of an external bias. In the latter role, they achieve up to ≈100 K of temperature variation within the device area. This study observes increased modal splitting of two plasmon-phonon polariton hybrid modes with temperature, which is a manifestation of increased plasmon-phonon coupling strength. Additionally, this study also reports on the existence of a thermally excited hybrid plasmon-phonon mode. This work can open the door for future optoelectronic devices such as electrically switchable graphene mid-infrared plasmon sources.