Topological surface states in a deformed chiral photonic crystal

Topological surface states (TSSs) in a three-dimensional (3D) chiral woodpile photonic crystal (PhC) with layer displacement are experimentally investigated in the microwave regime. Both the original layered chiral PhC and the structure with an in-plane displacement of one of the periodic layers host Weyl points that give rise to TSSs. Microwave transmission measurements of the deformed chiral PhC show a clear edge localization of the TSSs, which is consistent with the numerical simulations. Further numerical calculations reveal that the frequencies and wavevectors of the Weyl points and the associated TSSs can be systematically tuned by the layer displacement. By scaling the 3D structure down to the nanoscale, the TSSs and their displacement-induced tunability can be extended to the near-infrared and visible optical regimes.