Fig. 2: Electrical spectroscopy measurements and simulations.
a Normalized photocurrent spectrum of device 2 at several Fermi energies. The photocurrent spectra are normalized to the spectrum at the charge neutrality point (CNP). The polaritonic peaks are labeled by red arrows. The highlighted spectral regions in green correspond to the upper and lower reststrahlen bands (RB) of hBN and, in yellow to the SiO2 RB. The curves are offset for clarity. b Optical (FDTD) simulation of the graphene absorption spectrum for different Fermi energies normalized to the spectrum at CNP. We label the identified peaks in the same manner as the experimental ones in panel (a). c–f Cross-sectional view of the simulated electric field intensity normalized to the incident one across a region containing two metal nanorods, for wavelengths 10.2, 11.9, 12.2, and 13.3 μm corresponding to peaks 4, 5, 6, and 8, respectively in panel (a). The x − (horizontal) and z − (vertical) directions are defined in Fig. 1e. The white scale bar corresponds to 40 nm. The calculations consider a non-uniform graphene Fermi level with a value of 0.4 eV above the metal (for a detailed doping profile, see Supplementary Fig. 2). g–j Same as panels (c–f), but the simulations instead show the cross-sectional view of the x-component of the electric field normalized to the incident one. The black scale bar corresponds to 40 nm. k Dispersion relation of the polaritonic modes with the respective harmonic diffraction orders (2πn/D). The three horizontal dashed lines correspond to the defect resonance (n = 1/2), first (n = 1), and second (n = 2) diffraction order resonances launched by the metal rod array, respectively. The marked red dots represent the experimental values, which the numeric labels are defined in Fig. 2a. The graphene Fermi level is 0.4 eV. At the hBN RBs (green highlighted regions), the black, blue, orange, and purple lines correspond to the 1st, 2nd, 3rd, and 4th hybridized polaritonic modes, respectively. In yellow is highlighted the SiO2 RB.
