Flat bands and quasi-bound states in the continuum in a photonic Moir? lattice

This paper proposes flat bands and quasi-bound states in the continuum (Q-BIC) in a moire lattice. In addition to the inter-layer coupling and small rotation angle, we show that the inter-node coupling in a single-layer moire lattice can be controlled to obtain moire flat bands. Unlike any flat bands reported in lattices such as kagome, rhombus, Lieb, and stub, we show that the moire lattice exhibits both singular and non-singular flat bands simul-taneously. We investigate the flat band's eigenmodes to confirm their flatness and assess their singularity. The robustness of the flat bands to variation of background permittivity epsilon b is studied. Moreover, by further engineering the inter-node distance, the moire flat band states change to a quasi-bound state at a non-zero wave vector. The Q-BIC exhibit an ultra-high quality factor (Q-factor) of 2.7142 x 106, ultra-low mode volume of 0.214318 mu m3, and very narrow linewidth centred at 350.54 THz. We demonstrate the capability of the Q-BIC for lasing and nanocavity applications. Our results show that a single-layer photonic moire lattice provides a suitable platform to explore fundamental phenomena related to flat band systems. (c) 2023 Optica Publishing Group

Automated summary

This paper proposes the existence of flat bands and quasi-bound states in a moire lattice. Through controlling the inter-node coupling, the moire flat bands can be obtained. The moire lattice exhibits both singular and non-singular flat bands simultaneously. The Q-BIC in the moire lattice shows ultra-high quality factor, ultra-low mode volume, and very narrow linewidth, making it suitable for lasing and nanocavity applications.