Strong interlayer coupling and stable topological flat bands in twisted bilayer photonic Moiré superlattices

The moiré superlattice of misaligned atomic bilayers paves the way for designing a new class of materials with wide tunability.In this work,we propose a photonic analog of the moiré superlattice based on dielectric resonator quasi-atoms.In sharp contrast to van der Waals materials with weak interlayer coupling,we realize the strong coupling regime in a moiré superlattice,characterized by cascades of robust flat bands at large twist-angles.Surprisingly,we find that these flat bands are characterized by a non-trivial band topology,the origin of which is the moiré pattern of the resonator arrangement.The physical manifestation of the flat band topology is a robust one-dimensional conducting channel on edge,protected by the reflection symmetry of the moiré superlattice.By explicitly breaking the underlying reflection symmetry on the boundary terminations,we show that the first-order topological edge modes naturally deform into higher-order topological corner modes.Our work pioneers the physics of topological phases in the designable platform of photonic moiré superlattices beyond the weakly coupled regime.