A perspective of twisted photonic structures

Moiré superlattices - twisted van der Waals (vdW) structures with small angles - are attracting increasing attention in condensed matter physics, due to important phenomena revealed therein, including unconventional superconductivity, correlated insulating states, and ferromagnetism. Moiré superlattices are typically comprised of atomic layers of vdW materials where the exotic physics arises from quantum electronic coupling between adjacent atomic layers. The abundant phenomena revealed in moire electronics have motivated intensive studies on their photonic counterpart. In addition to vdW materials, twisted photonic systems can also be comprised of metamaterials, metasurfaces, and photonic crystals, mediated by interlayer electromagnetic coupling instead. The interplay between short-ranged interlayer quantum and long-ranged electromagnetic coupling in twisted structures is expected to yield rich phenomena in nano-optics. This study reviews recent progress in twisted structures for nanophotonics and outlook for emerging topics, opportunities, fundamental challenges, and potential applications.