Fig. 2: Topological transition of hybrid polaritons revealed by nanoimaging.
From: Doping-driven topological polaritons in graphene/α-MoO3 heterostructures
a–c, Experimentally measured polariton near-field amplitude (S3) images with graphene doping EF = 0 eV (a), EF = 0.3 eV (b) and EF = 0.7 eV (c). The polaritons were launched by a gold antenna. The α-MoO3 film was placed on top of a 300 nm SiO2/500 μm Si substrate. d–f, Absolute value of the spatial Fourier transforms (FTs) of the experimental near-field images shown in a–c, respectively, revealing the isofrequency contours of hybrid polaritons. The grey curves represent calculated isofrequency contours. g–i, Experimentally measured polariton near-field amplitude (S3) images with graphene doping EF = 0 eV (g), EF = 0.3 eV (h) and EF = 0.7 eV (i) for an α-MoO3 film placed on a 60 nm Au/500 μm Si substrate. The canalized wavefronts were measured at a graphene Fermi energy close to the value at which the topological transition occurs (h), showing deep-subwavelength and diffractionless polariton propagation. j–l, Absolute value of the FTs of the experimental near-field images in g–i, respectively. The grey curves show the calculated isofrequency contours. The α-MoO3 thickness was 140 nm in all panels. The incident light wavelength was fixed at λ0 = 11.11 μm (900 cm−1). Each colour scale applies to all images in the respective column.
