Robust moir\'e flatbands within a broad band-offset range

TL;DR

This paper introduces a method to tune and stabilize flatbands in photonic moiré superlattices by adjusting band offsets, enabling control over localized modes for advanced light-matter interactions.

Contribution

The study presents a novel approach to control flatbands in photonic moiré superlattices through band offset tuning, demonstrating robustness over a broad range.

Findings

Robust flatbands are formed at specific stacking sites.

Flatbands can be tuned or made to disappear by adjusting band offset.

The method enables high-quality localized modes with tunable frequencies.

Abstract

Photonic analogs of the moir\'e superlattices mediated by interlayer electromagnetic coupling are expected to give rise to rich phenomena such as nontrivial flatband topology. Here, we propose and demonstrate a scheme to tune the flatbands in a bilayer moir\'e superlattice by employing the band offset. The band offset is changed by fixing the bands of one slab while shifting those of the other slab, which is accomplished by modifying the thickness of the latter slab. Our results show that the band-offset tuning not only makes some flatbands emerge and disappear, but also leads to two sets of flatbands that are robustly formed even with the change of band offset over a broad range. These robust flatbands form either at the AA-stack site or at the AB-stack site, and as a result, a single-cell superlattice can support a pair of high-quality localized modes with tunable frequencies. Moreover, we develop a diagrammatic model to provide an intuitive insight into the formation of the robust flatbands. Our work demonstrates a simple yet efficient way to design and control complex moir\'e flatbands, providing new opportunities to utilize photonic moir\'e superlattices for advanced light-matter interaction including lasing and nonlinear harmonic generation.