Probing the band structure of topological silicon photonic lattices in the visible spectrum

We study two-dimensional hexagonal photonic lattices of silicon Mie resonators with a topological optical bandstructure in the visible spectral range. We use 30 keV electrons focused to nanoscale spots to map the local optical density of states in topological photonic lattices for the first time with deeply subwavelength resolution. By slightly shrinking or expanding the unit cell, we form hexagonal superstructures and observe the opening of a bandgap and a splitting of the double-degenerate Dirac cones, which correspond to topologically trivial and non-trivial phases. Optical transmission spectroscopy shows evidence of topological edge states at the domain walls between topological and trivial lattices.