Terahertz Topological Edge States and Corner States in Metallic Photonic Crystals

Topological photonic insulators have the capability of supporting edge states, which are mostly confined at the domain walls and immune to backscattering. Here we propose a metallic photonic crystal in two dimensional kagome lattice to realize the edge and corner states analog to valley Hall effect, which is realized by breaking the space symmetry through rotating the C-3-symmetry metallic scatters around the center of the unit cell. The work demonstrates that the terahertz (THz) waves are mainly located at the interface and propagate with weak backscattering. Even if the structural defects and sharp bends are introduced, the waves can also propagate smoothly. Besides, the corner states are also observed in this kagome lattice. The work will be beneficial for the development of the THz integrated devices with high transmission and robustness.