Dual-band topological surface states and multichannel photonic routings in three-dimensional chiral Weyl metamaterials

Recent advances in photonic structures with three-dimensional (3D) Weyl points offer exciting opportunities for exploring nontrivial Fermi arc surface states and enabling novel light-manipulation capabilities. However, previous studies mainly focused on exploring Fermi arc surface states operating in a single frequency band, leading to limited potential applications in multiband topological photonic routing, wave division, switching, and so on. Here, we demonstrate the existence of dual-band topological Fermi arc surface states in the 3D chiral photonic Weyl metamaterials. The dual-band gap mode physics originates from the Weyl points of different frequencies and the time-reversal symmetry is preserved. Through rigorous theoretical analysis, we study the size of the dual-band gaps that vary with the parameter ${k}_{z}$ and reveal the Weyl points as the critical points for topological phase transitions. Remarkably, the bandwidth-controllable, highly localized, and unidirectional dual-band Fermi arc surface states appear when the chiral metamaterials are in contact with the vacuum state. Moreover, a type of four-channel reconfigurable and multiband topological photonic routings is demonstrated utilizing the dual-band Fermi arc surface states. We reveal that the physical mechanism of realizing the multichannel reconfigurable topological pathways is caused by the frequency-chirality-locking of the highly localized Fermi arc surface states. Our work could offer insights into 3D Weyl semimetals and provide more flexibility for multiband topological photonic routings.