Visible Wavelength Flatband in a Gallium Phosphide Metasurface

Engineering the dispersion of light in a metasurface allows for controlling the light–matter interaction strength between light confined in the metasurface and materials placed within its near-field. Specifically, engineering a flatband dispersion increases the photonic density of states, thereby enhancing the light–matter interaction. Here, we experimentally demonstrate a metasurface with a flat dispersion at visible wavelengths. We designed and fabricated a suspended one-dimensional gallium phosphide metasurface and measured the photonic band structure via energy-momentum spectroscopy, observing a photonic band that is flat over 10° of half angle at ∼590 nm. We integrated cadmium selenide nanoplatelets with the metasurface and measured coupled photoluminescence into the flatband. Our demonstration of a photonic flatband enables the possibility of integrating emerging quantum emitters to the metasurface with possible applications in nonlinear image processing and topological photonics.