Nanophotonics with multilayer van der Waals materials

The field of nanophotonics requires high-quality materials for the fabrication of resonant structures that can confine light down to the nanoscale. Metallic nanostructures often used for this purpose exhibit high optical losses, so high-refractive-index dielectrics such as silicon (Si) and III–V semiconductors are widely used instead. Recently, layered materials, often referred to as ‘van der Waals materials’ for the forces holding atomic planes together in bulk crystals, have been introduced as alternative dielectric building blocks for nanophotonics. Compared to traditional semiconductors, these materials exhibit higher refractive indices and transparency in the visible and near-infrared favourable for compact waveguides; strong birefringence and large nonlinear optical coefficients attractive for nonlinear optics; and out-of-plane van der Waals adhesive forces enabling novel tuning techniques and heterointegration approaches for the realization of previously inaccessible photonic structures. Recently, these properties of quasi-bulk van der Waals materials (as opposed to their widely studied monolayers) have been applied in a variety of photonic structures and devices, which will be discussed here. We report on recent progress in utilizing layered materials in waveguiding, wavefront shaping, Purcell enhancement, quantum nanophotonics, lasing, nonlinear optics, and strong light–matter coupling, as well as offer a snapshot of future developments in hybrid and tunable nanophotonics, three-dimensional photonic structures, optical trapping, polariton devices and van der Waals integrated nanophotonic circuits.