Schematic of the cross-section of the 1D polaritonic nanostructure composed of two adjacent SSH lattices. The dashed line represents the physical boundary between the two adjacent SSH lattices. In the insets, we can inspect the unit cells cross-sections of both SSH lattices and see how the inter- and intra-cell distances are swapped relative to each other. The insets also show the real part of the polaritons out-of-plane electric field profile calculated slightly below 1,490 cm -1 for the experimental conditions of Dev-01. This is calculated using the effective refractive index scheme discussed in Supplementary Section 2.1 . The left inset shows an even field profile, whereas the other one shows an odd field profile. In the colour scheme, red and blue represent positive and negative values of the electric field, respectively, while zeros are depicted in white. Above the hBN flake surface is illustrated the presence of the sSNOM tip.
