Lattice-mismatch Moire laser with strong flatband coupling

Abstract

Inter-cell and/or interlayer coupling in Moire superlattices can generate flatbands and collective eigenmodes that enable emergent physical phenomena, motivating extensive exploration of Moire-inspired photonic devices. However, the experimental validation of robust inter-cell interactions in Moire photonic structures and the modulation of flatbands for specific photonic applications remain challenging. Here, we propose a lattice-mismatch Moire cavity and demonstrate nanolasers enabled by strong flatband coupling. In contrast to a twist-angle Moire cavity, a lattice-mismatch Moire cavity provides a stable flatband frequency and a substantial enhancement in Q factor compared to an isolated single-cell cavity, as the unit-cell size decreases. The photonic band-structure measurement of the small-unit-cell Moire cavity by photoluminescence reveals pronounced flatbands. Cell-resolved spectroscopy further confirms the presence of flatbands by identifying resonant peaks that consistently emerge across unit cells in a Moire cavity with a lattice mismatch of 102 nm, but not in a larger-unit-cell Moire cavity with a mismatch of 60 nm. Furthermore, mode selection is achieved by reducing the center-hole size, thus isolating the hexapole mode from the degenerate dipole modes while maintaining strong inter-cell coupling. Consequently, we demonstrate a low-threshold hexapole flatband laser in a single mode. Therefore, the systematic modification of the relative lattice parameters of the two constituent lattices offers a promising strategy for developing Moire nanolasers and flatband nanophotonic devices.