Fig. 2: Observation of the first-order photonic topological surface states.
From: Realization of a three-dimensional photonic higher-order topological insulator
a Photograph of the fabricated experimental sample comprising 4 unit cells in the y direction and 20 unit cells in the x and z directions. b The compositional layers are glided for photographing. Each unit cell (green square) comprises two perforated copper plate layers and two air foam layers inserted by metallic pillars (red circles) and dielectric rods (blue circles). c Schematic view of the projected 2D surface BZ. d Simulated surface (orange lines) and bulk (grey lines) state dispersions along high-symmetry lines. The cyan curve represents the light cone. e Measured transmission spectra of the surface (orange color) and bulk (grey color) states. The light beige regions represent the three photonic bandgaps. Measured (f) and simulated (g) electric field distributions of the topological surface states at 14.6 GHz. The cyan star represents the point source. h Measured (color map) and simulated (white dashed line) surface state dispersions along the high symmetry line.
