Spin-Type Photonic Topological Insulators on a Rhombic Lattice

A simplified model of a metallic spin-type photonic topological insulator on a rhombic lattice is presented and analyzed. Instead of the more commonly used hexagonal unit cells, a reduced symmetry rhombus is employed, which is both simpler and allows for easier integration into more traditional microwave systems. The non-trivial nature of the transport is shown via direct calculation of the structure's spin-projected Berry curvature and Wilson loop spectra, as well as by a systematic investigation of a reduced symmetry tight-binding model based off the Kane-Mele Hamiltonian. Device implementations are shown for a range of non-trivial configurations.