Coexistence of topological type-II Weyl and triply degenerate points in a chiral photonic metamaterial

In this work, we report the coexistence of type-II Weyl points and triply degenerate points while taking the nonlocal effect into account in a chiral photonic metamaterial system. The chiral effect introduces a break in the spatial inversion symmetry, which is necessary for the generation of nodal points. These nodal points are symmetrically distributed on the ${k}_{z}$ axis and possess the time-reversal symmetry-protection mechanism. Remarkably, the projections of all nodal points are connected by a Fermi arc surface state, and it agrees well with the single monopole charges of these nodal points, which demonstrates the topological characteristics of the band degenerate points. We theoretically show that the localized Fermi arc can be formed at the interface between the metamaterial and vacuum, which may improve the compactness of photonic devices. Especially, the nonreciprocal surface waves can propagate forward around the sharp corner without experiencing backscattering, which can be used for the robust transmission of information.