Constant cutoff frequency of a two-dimensional photonic crystal composed of metallic rods and epsilon-near-zero materials

It is well known that a photonic crystal composed of metal rods in a dielectric background exhibits a cutoff frequency below which the propagation of light is forbidden. The cutoff frequency usually increases as the volume fraction of the metal rod increases. However, we report that the cutoff frequency of a photonic crystal composed of metal rods and an epsilon-near-zero material background is independent of the volume fraction and identical to the plasma frequency of the metal rod. The extremely long wavelength of light in an epsilon-near-zero material causes this interesting phenomenon.