Anisotropy-induced flattened dispersion and higher-order topology in C_2v symmetry triangular photonic crystals

Symmetry plays a fundamental role in topological photonic crystals, and topological phase transitions induced by disorder have also been extensively explored in recent years. However, in this work, we find anisotropy can be induced by reducing symmetry in a C _2v symmetry triangular photonic crystal. We investigate that anisotropy-induced interfaces profoundly affect edge states and enable the realization of slow light dispersion. Numerical simulations reveal a transition from gapless chiral edge modes to gapped flat band dispersion. Furthermore, we observe higher-order corner states in corner structures constructed by anisotropic interfaces. The corner states can be induced and localized at different lattice positions, thereby realizing multiple types of higher-order topological states. We demonstrate the significance of anisotropic geometry in topological photonics. These findings open new possibilities for steering wave transport in multiple dimensions and offer, to our knowledge, a novel research perspective on the transformation of topological states induced by anisotropic lattices.