Electromagnetic properties of a monolayer of polarisable particles deposited on graphene

Interesting plasmonic effects can arise from the combination of small polarisable particles with graphene, related to surface plasmon-polaritons (SPPs) supported by the latter in the terahertz (THz) spectral range. The electromagnetic coupling between graphene SPPs and dipole moments of nanoparticles (NPs) deposited on top of it gives rise to optical properties that aren’t present in the individual components of this system. The NPs’ polarisability is renormalized due to the electromagnetic back action of the SPPs which are excited in graphene when an external propagating electromagnetic wave impinges on the particle. Moreover, beyond the usual dipole-dipole interaction, an indirect particle-particle coupling arises via polarisation charges induced on the graphene-covered interface by each particle – this indirect coupling oscillates with the interparticle distance. We derived coupled-dipole equations taking into account all these effects, allowing us to calculate an effective optical conductivity of the particles’ monolayer. One of the G+NPs system’s unique properties is a collective polariton mode, causing a considerable enhancement of the THz radiation absorption in graphene, while the reflection drops to nearly zero for a broad range of angles of incidence. The frequency of this resonant mode can be adjusted by changing the Fermi energy in graphene via electrostatic gating and therefore it can be used for electrically controlled reflection and transmission of THz radiation