\textbf{Gyroid photonic crystal with Weyl points: synthesis and mid-infrared photonic characterization}

Weyl points are degenerate energy states resulting from crossings of linear bands in 3D momentum space. Unlike their 2D counterparts, Weyl points are bulk degenerate states that are stable to weak perturbation. The topological surface states associated with Weyl points exhibit unidirectional backscattering-immune transport. Double gyroid photonic crystals with a parity-breaking perturbation are predicted to possess Weyl points. We designed and synthesized single and double gyroid mid-IR photonic crystals composed of a-Si. We characterized them by mid-IR spectroscopy. We observed 100{\%} reflection at 8$\mu $m for single gyroids with unit cell size of 5$\mu $m, in agreement with the predicted photonic bandgap seen in full-wave EM simulations. As the unit cell size of single gyroids changes to 6$\mu $m, the observed reflection peak shifted to 9$\mu $m, also agreeing with simulation. For double gyroids with unit cell size of 5$\mu $m, we observed a 20{\%} decrease in reflection at 8$\mu $m, which could be explained by a new pair of states appearing within the bandgap from our simulation of double gyroids. We use angle-resolved mid-IR spectroscopy with a QCL to characterize Weyl points.