In the realm of moiré physics, the manipulation of flatbands plays a crucial role in shaping advanced light-matter interactions and unlocking phenomena like superconductivity and optical solitons. Traditionally, the generation of moiré flatbands relied on specific structures and careful control of rotation angles and spacings between lattice layers. However, a recent breakthrough by a collaborative research team from various universities in China has introduced a new method to control moiré flatbands by adjusting the band offset of two photonic lattices in the parameter space.
The team’s research, as reported in Advanced Photonics Nexus, revealed that by adjusting the band offset, two distinct groups of robust flatbands can be created within a broad range of band offset values. Unlike traditional flatbands that appear and disappear as the band offset changes, these robust flatbands remain steady. This discovery of stable flatbands offers greater flexibility and ease in obtaining nontrivial superlattices, opening doors to new opportunities in moiré photonics.
To achieve this breakthrough, the researchers began with a mismatched silicon-based bilayer moiré superlattice and manipulated the band offset by varying the thickness of one layer. By calculating the superlattice band structure at different band offsets, they observed the direct influence of band offset on the appearance and disappearance of moiré flatbands. Notably, they identified certain moiré flatbands that maintained stability within a broad range of band offsets, indicating the potential for resonance frequency adjustments by altering structural parameters.
The resonant frequencies of these robust flatbands can be modified by adjusting structural parameters, enabling the creation of innovative multiresonant moiré devices. This breakthrough holds promise in developing novel applications in areas such as laser emission and second harmonic generation. The researchers extensively investigated localized modes originating from the two groups of robust flatbands in finite-sized moiré superlattices, confirming the feasibility of high-quality doubly resonant moiré superlattices.
To shed light on the formation of robust flatbands, the authors proposed a simple yet effective diagrammatic model based on coupled-mode theory. This model took into account the structural characteristics of moiré superlattices and revealed both similarities and differences in the formation of these flatbands. Full-wave calculations were incorporated into the diagrammatic model, successfully predicting the field distribution of the robust flatbands.
The ability to control moiré flatbands by manipulating the band offset in parameter space offers an elegantly simple method to unlock nontrivial superlattices and delve into the mysteries of flatband emergence and disappearance. With the frequencies of these flatbands now within our command, a realm of multi-resonant and high-quality moiré superlattices emerges, paving the way for innovative moiré devices and further exploration of moiré physics.
The groundbreaking research by the collaborative team from Chinese universities has revolutionized the field of moiré photonics by introducing a novel approach to control moiré flatbands. By adjusting the band offset of photonic lattices in the parameter space, the researchers demonstrated the creation of two groups of robust flatbands that offer stability within a broad range of band offsets. This discovery provides new avenues for the development of advanced moiré devices and opens up unexplored possibilities in the captivating realm of moiré physics.