title: Gyroid Optical Metamaterials: Calculating the Effective Permittivity of Multidomain Samples.
abstract: Gold gyroid optical metamaterials are known to possess a reduced plasma frequency and linear dichroism imparted by their intricate subwavelength single gyroid morphology. The anisotropic optical properties are, however, only evident when a large individual gyroid domain is investigated. Multidomain gyroid metamaterials, fabricated using a polyisoprene-b-polystyrene-b-poly(ethylene oxide) triblock terpolymer and consisting of multiple small gyroid domains with random orientation and handedness, instead exhibit isotropic optical properties. Comparing three effective medium models, we here show that the specular reflectance spectra of such multidomain gyroid optical metamaterials can be accurately modeled over a broad range of incident angles by a Bruggeman effective medium consisting of a random wire array. This model accurately reproduces previously published results tracking the variation in normal incidence reflectance spectra of gold gyroid optical metamaterials as a function of host refractive index and volume fill fraction of gold. The effective permittivity derived from this theory confirms the change in sign of the real part of the permittivity in the visible spectral region (so, that gold gyroid metamaterials exhibit both dielectric and metallic behavior at optical wavelengths). That a Bruggeman effective medium can accurately model the experimental reflectance spectra implies that small multidomain gold gyroid optical metamaterials behave both qualitatively and quantitatively as an amorphous composite of gold and air (i.e., nanoporous gold) and that coherent electromagnetic contributions arising from the subwavelength gyroid symmetry are not dominant.
authors: Department of Engineering, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0FA, U.K.; Nanophotonics Centre, Department of Physics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, U.K.
authors: James A
authors: JA
authors: Dolan
authors: Department of Physics, Imperial College , Prince Consort Road, London SW7 2BB, U.K.
authors: Matthias
authors: M
authors: Saba
authors: Nanophotonics Centre, Department of Physics, University of Cambridge , J.J. Thomson Avenue, Cambridge CB3 0HE, U.K.
authors: Raphael
authors: R
authors: Dehmel
authors: Adolphe Merkle Institute , Chemin des Verdiers 4, 1700 Fribourg, Switzerland.
authors: Ilja
authors: I
authors: Gunkel
authors: Department of Materials Science and Engineering, Cornell University , 330 Bard Hall, Ithaca, New York 14853-1501, United States.
authors: Yibei
authors: Y
authors: Gu
authors: Department of Materials Science and Engineering, Cornell University , 330 Bard Hall, Ithaca, New York 14853-1501, United States.
authors: Ulrich
authors: U
authors: Wiesner
authors: Department of Physics, Imperial College , Prince Consort Road, London SW7 2BB, U.K.
authors: Ortwin
authors: O
authors: Hess
authors: Department of Engineering, University of Cambridge , J.J. Thomson Avenue, Cambridge CB3 0FA, U.K.
authors: Timothy D
authors: TD
authors: Wilkinson
authors: Nanophotonics Centre, Department of Physics, University of Cambridge , J.J. Thomson Avenue, Cambridge CB3 0HE, U.K.
authors: Jeremy J
authors: JJ
authors: Baumberg
authors: Adolphe Merkle Institute , Chemin des Verdiers 4, 1700 Fribourg, Switzerland.
authors: Ullrich
authors: U
authors: Steiner
authors: Adolphe Merkle Institute , Chemin des Verdiers 4, 1700 Fribourg, Switzerland.
authors: Bodo D
authors: BD
authors: Wilts
keywords: block copolymer; effective medium model; gyroid; optical metamaterial; polymer self-assembly