Fig. 2: Bands and group velocities of the interface states.

a The interface bands of TE-like modes. The grey domain denotes the light cone, and the greyish-green domain denotes the projected bulk bands. The inset shows the supercell of the spliced structure, where the grey part is silicon film and the white triangles are holes. The translational parameter (red arrow) and the wavevector (blue arrow) along the interface are marked. b Group velocity as a function of parameter ξ and wavelength. The colored lines are group velocity lines for ξ = 0.52, 0.55, 0.58, 0.61, 0.64, 0.67, and 0.70, respectively. The zero-group-velocity plane is marked by the grey plane. The cyan region denotes the projection of group velocity lines. c Calculated results of interface intensity for different incident wavelengths. The green dashed lines mark the boundaries of the projected interface bands, where the dimension ξ is substituted by the coordinate y.