Observation of Square‐Root Higher‐Order Topological States in Photonic Waveguide Arrays
Observation of Square‐Root Higher‐Order Topological States in Photonic Waveguide Arrays
Abstract Recently, higher‐order topological insulators (HOTIs), accompanied by topologically nontrivial boundary states with a codimension larger than one, have been extensively explored because of unconventional bulk‐boundary correspondences. As a novel type of HOTIs, very recent works have explored the square‐root HOTIs, where the topologically nontrivial nature of bulk bands stems …