Fig. 3: Modal order transition of HPhPs in hBN/InAs heterostructure.
From: Polariton design and modulation via van der Waals/doped semiconductor heterostructures
a The relationship between normalized kHPhP and InAs ωp. All curves are calculated by Eq. (1), while all symbols are experimental data. Solid symbols represent fundamental modes, while open symbols represent high-order modes. Data with dielectric (metallic) InAs are plotted with black (purple) symbols. The colored shades indicate whether InAs behaves as dielectrics or metals. b The modal order transition observed in the frequency ___domain. The contour plot is calculated by TMM and triangles are experimental data. For experimental data points above the transitional frequency, a different method is employed to extract wavevectors due to high polaritonic loss, and details are given in Supplementary Note 7. The yellow dashed curve is calculated with the analytical solution (Eq. (1)). c kHPhP at different wavenumber and InAs ωp, with larger kHPhP plotted with the brighter color. The modal order clearly transits when InAs ωp passes the Reststrahlen band of hBN, and the transition is noted with the green dashed curve. d Three representative s-SNOM images (optical amplitude, S) plotted with the same scale bar showing the engineered kHPhP. The corresponding working frequency and InAs ωp are noted as numbers in the (c). While the hBN thickness in subpanel−1 is 51 nm, the hBN thickness in subpanel-2,3 is 75 nm. The normalized wavevectors for the three subpanels are 0.235, 1.35, and 0.24, respectively. The nature of this tuning is the interaction between the evanescent field of HPhPs and the substrate, as indicated by the Eq. (2), and intuitively shown in Supplementary Fig. 18.
