Realization of a Photonic Higher-Order Double-Weyl Semimetal

Higher-order Weyl semimetal (HOWSM) with coexisting 2D topological surface states and 1D topological hinge states establishes the fundamental connection between the Weyl physics and higher-order topology. However, existing experimental demonstrations of HOWSM have primarily focused on Weyl nodes with chiral charges of ±1. In this work, based on the space group symmetry, a photonic higher-order double-Weyl semimetal (HODWSM) with larger chiral charges is theoretically designed and experimentally realized in a 3D photonic metamaterial. It is demonstrated that this photonic HODWSM exhibits a single pair of quadratic double-Weyl points with chiral charges of ±2 in the $k_z=0$ plane, supporting nontrivial higher-order band topology in the remaining k_z planes and achieving unprecedentedly long hinge Fermi arc traversing the entire Brillouin zone. This work extends the research scope of HOWSM and offers an ideal photonic platform for exploring higher-order Weyl physics.