It is recognized that for a certain class of periodic photonic crystals, conical dispersion can be related to a zero-refractive index. It is not obvious whether such a notion can be extended to a noncrystalline system. We show that certain photonic quasicrystalline approximants have conical dispersions at the zone center with a triply degenerate state at the Dirac frequency, which is the necessary condition to qualify as a zero-refractive-index medium. The states in the conical dispersions are extended and have a nearly constant phase. Experimental characterizations of finite-sized samples show evidence that the photonic quasicrystals do behave as a near zero-refractive-index material around the Dirac frequency.
American Physical Society
Physical Review Letters
Scientific Computing

Dong, J., Chang, M., Huang, X., Hang, Z., Zhong, Z., Chen, W., … Huang, Z. (2015). Conical Dispersion and Effective Zero Refractive Index in Photonic Quasicrystals. Physical Review Letters, 114(16).