Angle-Resolved Mid-Infrared Spectroscopy of Gyroid Photonic Crystals

Gyroid photonic crystals, which can form photonic topological insulators, offer a richdiversity of physics for fundamental study, in addition to yielding useful applications.Understanding their band structure is crucial towards advancing both fronts. Anangle-resolved spectroscopy apparatus is constructed to experimentally measureband structures. Operating at wavelengths from 7.7 to 11.1 μm, it is employed tostudy single and double-gyroid photonic crystals, constructed of amorphous siliconin 5 μm unit cells. Transmittance and reflectance act as indicators of density ofstates, and are collected as spectra over angles of incidence ranging from 17 to 30degrees. Comparison to theory confirms interesting features, such as bandgaps.Further simulation guides the design of a crystal amenable to the first experimentalmeasurement of Weyl points at mid-infrared wavelengths.