Plasmonic Resonant Absorption in Mid-Infrared in Graphene Nanoresonators

We experimentally demonstrated polarization-sensitive, tunable plasmonic resonant absorption in the mid-infrared range of 5-14 um by utilizing an array of graphene nanoribbon resonators. By tuning resonator width and charge density, we probed graphene plasmons with $\lambda_{\mathrm{p}}$ $\le \lambda $/100 and plasmon resonance energy as high as 0.26 meV (2100 cm$^{-1})$ for 40 nm wide nanoresonators. Resonant absorption spectra enabled us to map the wavevector-frequency dispersion for graphene plasmons at mid-IR energies and revealed a modified plasmon dispersion as well as plasmon damping due to intrinsic optical phonons of graphene and graphene plasmon interaction with the surface polar phonons in SiO$_{2}$ substrates. Additionally, we studied spectra further by introducing intrinsic defect phonons and doping by direct electron beam irradiation of graphene nanoresonators