Fig. 2: Device design and linear measurements.

a Schematic of metasurface nanostructure. Gold rods with dimensions of l = 1230 nm and w = 70 nm) are arrayed on the graphene with gaps of \({g}_{x}\) = 260 nm along the long axis and \({g}_{y}\) = 150 nm along the short axis. b SEM image of the gold rods (brighter) on graphene (darker). Scale bar is 500 nm. c Plot of measured spectra of transmission modulation, defined as \(1-T/{T}_{{CNP}}\) where \({T}_{{CNP}}\) is the transmission at the charge neutral point. Spectra for different Fermi energies are plotted, and a clear increase in transmission modulation is seen around 7.5 and 11.5 \(\mu m\), corresponding to graphene-like plasmon resonances. The black dashed vertical line corresponds to the wavelength of the charge maps in (d). d Calculated charge density oscillation map at 7.5 μm excitation at the CNP (left panel) and at higher doping (0.35 eV) (right panel). At higher doping, strong charge oscillations are concentrated on the graphene between the tips of the gold rods, indicating a graphene-like resonance.