Fig. 3: Normalized photocurrent spectra of device 3 at the hBN RBs.

a Normalized photocurrent spectra at the upper RB of hBN for several gate voltages. The photocurrent spectra are normalized to the spectrum at CNP. The polaritonic peaks are labeled by red arrows. The 0.20 eV curve is slightly shifted (divided by 1.05) for illustration. The Fermi energies are presented in absolute values. b Same as panel (a) but for the lower RB range. c Optical simulation of graphene absorption at the upper RB spectral region for different Fermi energies normalized to the spectrum at CNP. We label the identified peaks in the same manner as the experimental ones. d Same as panel (c) but for the lower RB range. e Cross-sectional view of the electric field intensity normalized to the incident one. The x − (horizontal) and z − (vertical) directions are defined in Fig. 1e. The simulations correspond to a non-uniform graphene Fermi level at 0.35 eV at wavelength 6.91 μm (corresponding to peak 1' in panel (a). The white scale bar corresponds to 20 nm. f Same as panel (e) but for a lower RB range at wavelength 12.37 μm (corresponding to peak 4' in Fig. 3b).