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

TL;DR

This paper introduces a photonic moiré superlattice with strong interlayer coupling, exhibiting robust topological flat bands and edge states, advancing the understanding of topological phases in tunable photonic systems.

Contribution

It demonstrates the realization of strong coupling and topologically non-trivial flat bands in a photonic moiré superlattice, a significant departure from weakly coupled van der Waals materials.

Findings

Presence of cascades of robust flat bands at large twist angles.

Flat bands exhibit non-trivial topological properties.

Edge and corner modes depend on symmetry breaking.

Abstract

The moir\'e 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 moir\'e 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 moir\'e 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 moir\'e 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 moir\'e 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 moir\'e superlattices beyond the weakly coupled regime.