When monolayer graphene was first exfoliated, it was described as a playground for condensed-matter physicists and materials scientists1. Since then, the landscape has expanded with the introduction of a diverse family of two-dimensional (2D) van der Waals (vdW) materials with properties ranging from wide-bandgap insulators — such as hexagonal boron nitride — to superconductors and magnets, as well as a whole palette of transition metal dichalcogenide semiconductors with bandgaps spanning the visible to the mid-infrared range. Moreover, the stacking or lateral alignment of these 2D vdW materials into homostructures and heterostructures enables the fabrication of devices with diverse functionalities in electronics, photonics and spintronics.

Credit: Luojun Du

Furthermore, 2D vdW materials provide an additional degree of freedom through the twist angle. By changing the lattice alignment of vertically stacked 2D vdW materials — either by twisting the angle or by creating lateral lattice mismatches — moiré superlattices with tunable periodic potentials arise, allowing the engineering of the band structure. Prime examples are the field-defining reports of unconventional superconductivity and correlated insulator behaviour in magic-angle graphene superlattices2,3. These studies have inspired intense activity to expand the fundamental understanding of the properties of moiré superlattices and harness their unique features in electronic, photonic and magnetic devices. In a Review Article in this issue of Nature Materials, Luojun Du and colleagues provide context for the recent advances in the field, from the perspective of nonlinear electronics (such as the nonlinear Hall effect and the photogalvanic effect) and nonlinear optics (such as second-harmonic generation and polariton–polariton interactions). The authors discuss the key challenges towards practical applications, such as achieving precise control of the twist angle at the wafer scale and minimizing impurities and strain disorder, and discuss the opportunities that moiré superlattices offer, focusing particularly on their technological potential in on-chip nanophotonics, optical communications, metrology and quantum information.

Beyond photonics, in a Picture Story in this issue, we highlight a moiré transistor that functions as a room-temperature neuromorphic device4. It is based on an asymmetric bilayer graphene/hexagonal boron nitride moiré heterostructure and works by the gate-controllable dynamic interplay between the electrons localized by a moiré potential and the itinerant electrons in conductive channels. The gate-tunable, room-temperature operation brings opportunities towards complex electronic applications.

Furthermore, the rapid advancements in moiré superlattice research with 2D vdW materials are now inspiring similar investigations in alternative material platforms and related fields. For instance, 2D halide perovskites can be exfoliated, transferred and stacked into homostructures and heterostructures comparable to vdW materials. Adding the tuning knob of a moiré potential can unlock additional functionalities and provide control. Writing in an Article in this issue, Shuchen Zhang and colleagues report the formation of square moiré superlattices with varying periodic lengths in twisted, ultrathin, ligand-free halide perovskite films, which exhibit localized bright excitons, trapped charge carriers and enhanced exciton emission. In an accompanying News & Views article, William Tisdale discusses the crucial role of the synthesis method for the ligand-free 2D perovskites developed by Zhang and colleagues, which enables the realization of twisted perovskite homobilayers exhibiting a moiré potential and a twist-angle dependence for exciton diffusion, light emission and electrical conduction. Tisdale further examines the prospects of high-brightness light emitters, optical sensors and indistinguishable single-photon emitters for quantum information applications using 2D halide perovskite moiré superlattices, alongside the numerous ongoing challenges in this emerging field, such as the fabrication of moiré heterobilayer perovskites or the exploration of perovskite-based moiré superlattices.

Photonic and phononic crystals and metamaterials typically consist of regular 2D lattices. With their simplified fabrication, stacking and characterization, they provide an inherently suitable platform for exploring the opportunities offered by engineering the twist-angle degree of freedom. In a Perspective article, Mourad Oudich and colleagues discuss how discoveries in vdW moiré superlattices are inspiring photonics and phononics researchers to develop synthetic structures with advanced functionalities. These structures utilize twist-angle engineering to manipulate the propagation of classical waves, which can be used in applications in nanophotonics, topological photonics and acoustofluidics.

Although challenges around scalability and reproducibility need to be addressed before moiré superlattices move from lab to fab, strides are being made5,6. In the meantime, we anticipate a continuous stream of exciting fundamental discoveries and proof-of-concept functional devices emerging from research labs.