Abstract
We systematically study the first- and second-order band topologies, which are tied to the pseudospin and valley degree of freedoms (DOFs), in honeycomb-kagome photonic crystals (HKPCs). We first demonstrate the quantum spin Hall phase as the first-order pseudospin-induced topology in HKPCs by observing the partial pseudospin-momentum locked edge states. By employing the topological crystalline index, we also discover the multiple corner states emerging in the hexagon-shaped supercell as the manifestation of the second-order pseudospin-induced topology in HKPCs. Next, by gapping the Dirac points, a lower band gap associated with the valley DOF emerges, in which the valley-momentum locked edge states are observed as the first-order valley-induced topology. Such HKPCs without inversion symmetry are proved to be Wannier-type second-order topological insulators, which manifested with valley-selective corner states. Additionally, we also discuss the symmetry breaking effect on pseudospin-momentum locked edge states. Our work realizes both pseudospin-induced and valley-induced topologies in a higher-order manner and thus provides more flexibility in manipulating electromagnetic waves, which may find potential applications in topological routings.
Funder
National Natural Science Foundation of China
Subject
Atomic and Molecular Physics, and Optics
Cited by
2 articles.
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