title: Amorphous diamond-structured photonic crystal in the feather barbs of the scarlet macaw.
abstract: Noniridescent coloration by the spongy keratin in parrot feather barbs has fascinated scientists. Nonetheless, its ultimate origin remains as yet unanswered, and a quantitative structural and optical description is still lacking. Here we report on structural and optical characterizations and numerical simulations of the blue feather barbs of the scarlet macaw. We found that the sponge in the feather barbs is an amorphous diamond-structured photonic crystal with only short-range order. It possesses an isotropic photonic pseudogap that is ultimately responsible for the brilliant noniridescent coloration. We further unravel an ingenious structural optimization for attaining maximum coloration apparently resulting from natural evolution. Upon increasing the material refractive index above the level provided by nature, there is an interesting transition from a photonic pseudogap to a complete bandgap.
authors.affiliation: Department of Physics, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, People's Republic of China.
authors.forename: Haiwei
authors.initials: H
authors.lastname: Yin
authors.forename: Biqin
authors.initials: B
authors.lastname: Dong
authors.forename: Xiaohan
authors.initials: X
authors.lastname: Liu
authors.forename: Tianrong
authors.initials: T
authors.lastname: Zhan
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.forename: Jian
authors.initials: J
authors.lastname: Zi
authors.forename: Eli
authors.initials: E
authors.lastname: Yablonovitch
mesh_terms: D000818:Animals; D003460:Crystallization; D005241:Feathers / Q000737:chemistry* / Q000648:ultrastructure*; D007633:Keratins / Q000737:chemistry*; D008543:Melanins / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D055095:Optics and Photonics; D010311:Parrots / Q000033:anatomy & histology*; D010858:Pigmentation; D012031:Refractometry; D014617:Vacuoles / Q000737:chemistry / Q000648:ultrastructure
chemical_list: D008543:Melanins; D007633:Keratins