Weyl fermions have not been found in nature as elementary particles, but they emerge as nodal points in the band structure of electronic and classical wave crystals. Novel phenomena such as Fermi arcs and chiral anomaly have fueled the interest in these topological points which are frequently perceived as monopoles in momentum space. We demonstrate that generalized Weyl points can exist in a parameter space and we report the first observation of such nodal points in one-dimensional photonic crystals in the optical range. The reflection phase inside the band gap of a truncated photonic crystal exhibits vortexes in the parameter space where the Weyl points are defined and they share the same topological charges as the Weyl points. These vortexes also guarantee the existence of interface states, the trajectory of which can be understood as “Fermi arcs” emerging from the Weyl nodes.
Hui Liu, Qiang Wang, Meng Xiao, Shi Ning Zhu, and Che Ting Chan, "Experiment of synthetic Weyl points in optical regime (Conference Presentation)," Proc. SPIE 10343, Metamaterials, Metadevices, and Metasystems 2017, 103431M (Presented at SPIE Nanoscience + Engineering: August 09, 2017; Published: 21 September 2017); https://doi.org/10.1117/12.2273637.5583321745001.
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