Experimental observation of gapless and gapped nodal rings in two-dimensional photonic crystals
Phys. Rev. Applied 23, 064064 – Published 27 June, 2025
DOI: https://doi.org/10.1103/fckg-br2d
Abstract
Nodal line semimetals exhibit band degeneracies that manifest themselves as one-dimensional ring structures in the momentum space. Here we experimentally demonstrate the existence of both gapless and gapped nodal rings in a two-dimensional photonic crystal composed of all-dielectric material. Breaking mirror symmetry that introduces a mass term causes the nodal ring degeneracies to transition into gapped states. By stacking two photonic crystals with opposite mass terms, we observe the emergence of Jackiw-Rebbi-like interface states within the gapped nodal rings. These interface states exhibit flat band dispersion, which is used to realize slow-light waveguides with low propagation loss. Additionally, a mode-tapering waveguide is designed by our modulating both the size of the gapless nodal ring structure and the bandwidth of the gapped nodal rings. Our results provide a simple two-dimensional platform for investigating nodal ring physics and exploring the potential applications of nodal rings in photonic devices.
