title: Conical dispersion and effective zero refractive index in photonic quasicrystals.
abstract: 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.
authors.affiliation: School of Physics and Engineering and State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275, China.
authors.forename: Jian-Wen
authors.initials: JW
authors.lastname: Dong
authors.affiliation: School of Physics and Engineering and State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275, China.
authors.forename: Ming-Li
authors.initials: ML
authors.lastname: Chang
authors.affiliation: Department of Physics and the Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Xue-Qin
authors.initials: XQ
authors.lastname: Huang
authors.affiliation: Department of Physics, Soochow University, 1 Shizi Street, Suzhou 215006, China.
authors.forename: Zhi Hong
authors.initials: ZH
authors.lastname: Hang
authors.affiliation: School of Physics and Engineering and State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275, China.
authors.forename: Zhi-Chao
authors.initials: ZC
authors.lastname: Zhong
authors.affiliation: School of Physics and Engineering and State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275, China.
authors.forename: Wen-Jie
authors.initials: WJ
authors.lastname: Chen
authors.affiliation: School of Physics and Engineering and State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275, China.
authors.forename: Zhan-Yun
authors.initials: ZY
authors.lastname: Huang
authors.affiliation: Department of Physics and the Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: C T
authors.initials: CT
authors.lastname: Chan