Multitype topological transitions and multichannel directional topological photonic routings in chiral metamaterials

The investigation of topological transitions has opened up unprecedented avenues for scientific exploration in photonic metamaterials. However, previous studies mainly focused on exploring different types of three-dimensional (3D) equifrequency surfaces and their topological transition processes in magnetic topological systems. In this work, we study the multiple photonic topological transitions and dual-frequency photonic Weyl points in the topological chiral metamaterials. Through effective medium theory and topological band theory, we systematically characterize and draw comprehensive topological phase diagrams associated with diverse 3D equifrequency surface configurations in nonmagnetic photonic systems. We further demonstrate that the resonance frequency ω0 and dual-frequency Weyl points are the critical points of these topological transitions. Notably, when the vacuum state is in contact with the phases I or III chiral metamaterials, the high-local and frequency chirality-dependent topological Fermi arc surface states arise. We reveal that the parameter ω can be used as a degree of freedom to regulate the bandwidth of such topological surface states. Moreover, different types of multichannel and directional topological photonic routings are achieved using the chirality-dependent Fermi arc surface states. We theoretically show that the physical mechanism of achieving these multichannel topological photonic routings is caused by the different interface properties. We could offer promising perspectives on 3D topological semimetal systems and provide more adaptability for multichannel devices in the nonmagnetic continuous media.