Topological phase transition induced by modulating unit cells in photonic Lieb lattice

TL;DR

This paper theoretically demonstrates how modulating unit cells in a gyromagnetic photonic Lieb lattice induces a hierarchy of topological phases, including first- and second-order states, with potential applications in robust photonic devices.

Contribution

It reveals a method to induce multiple topological phases in photonic lattices by breaking spatial symmetries, expanding the design possibilities for topological photonics.

Findings

Identification of topological phase transitions via bandgap closures

Realization of both edge and corner states in photonic crystals

Potential for disorder-resistant waveguides and integrated circuits

Abstract

Topological photonics was embarked from realizing the first-order chiral state in gyromagnetic media, but its higher-order states were mostly studied in dielectric lattice instead. In this paper we theoretically unveil a hierarchy of topological phases under broken time-reversal symmetry, which include the first-order Chern, and the second-order dipole, quadrupole phases. Concretely, by relaxing a certain spatial symmetry of unit cell, versatile topological phases including both edge and corner states can be established to transit around, with bandgap closures marking the phase boundaries. Our results on gyromagnetic photonic crystals may broaden the scope of sublattice engineering design for topological phase manipulation, potentially enabling multifunctional disorder-resistant waveguides and integrated photonic circuits for information communication.