Visible Flatbands in a Gallium Phosphide Metasurface

Tailoring the dispersion of light in a metasurface is a key aspect for determining the strength of light-matter interaction between the transiting light and a material placed within the near-field of the metasurface. Specifically, engineering a flat photonic band increases the density of states and enhances the light-matter coupling. Here, we experimentally demonstrate a flat photonic band over a range of input angles in the visible light regime by fabricating a gallium phosphide metasurface and measuring its photonic band structure using energy-momentum spectroscopy. We then integrate nanoplateletes resonant with the flatband and measure enhanced photoluminescence into the flatband of the device. This opens up the possibility for integration of nonlinear materials and flatband engineering of emitters.