Coexistence of Chiral Edge and Localized States in a High Chern Number Topological Photonic Alloy

Recently, a topological photonic alloy with a Chern number of 1 has been proposed and experimentally verified. Here, we create a substitutional-type topological photonic alloy system with a high Chern number of 2 coexisting with a Chern number of −1, based on the random mixing of nonmagnetized and magnetized yttrium iron garnet (YIG) rods. Interestingly, we find localized states in the topological gap with a high Chern number of 2, which is different from that of −1. These localized states fill the topological gap statistically, indicating that the gap with a high Chern number of 2 is not a density of states (DOS) gap. By further investigating the transport behavior of the chiral edge state (CES) in the topological gap, we find that the transport is unaffected. However, as observed through electromagnetic field inspections, the CESs may couple with these localized states during propagation. Our work deepens the understanding and further enriches the topological photonic alloy system.