Fig. 2: Nano-imaging of intersubband transition and hyperbolic plasmon polariton in WOx/4L-WSe2.
a Permittivity of the WSe2 (dashed lines) and with high carrier density under charge transfer (solid lines). Inset: the isofrequency surface modified from ellipse to a hyperboloid in the red-shaded region. Images of near-field scattering amplitude s(ω) for WOx/4L-WSe2 with excitation energy Eph = 144 meV (b) and Eph = 149 meV (c). The layer thickness is d ~ 4.5 nm. Scale bar: 500 nm. d Line traces of the interference pattern from the edge-reflected plasmon polariton taken from the near-field scattering amplitude image as illustrated in (b) and (c) (white dashed lines). Black dashed line marks the edge of the sample and red dashed line marks the peak position. e Dispersion of the intersubband polariton (ISP) in WOx/4L-WSe2. Color plot is calculated using the Fresnel reflection coefficients Im(rp). Yellow squares are experimental data. The error bars are determined from the fitting uncertainties of the fringe periodicities. f The extracted real part of momentum q as a function of carrier density n for WOx/4L-WSe2. The red solid line is the fit to the data using the relation \(q\approx 1/n\). The error bars are determined from the fitting uncertainties of the fringe periodicities. g Images of near-field scattering amplitude s(ω) for WOx/3L-WSe2 and WOx/5L-WSe2 with excitation energies Eph = 270 meV and Eph = 98 meV, respectively. Scale bar: 250 nm.
