Moiré excitons and exciton-polaritons: A review

Abstract: Distinguished by their long lifetimes, strong dipolar interactions, and periodic confinement, moir\'e excitons provide a fertile territory for realizing interaction-driven excitonic phases beyond conventional semiconductor systems. Formed in twisted or lattice-mismatched van der Waals heterostructures, these excitons are shaped by a periodic potential landscape that enables the engineering of flat bands, strong interactions, and long-lived localised states. This has opened pathways to explore strongly correlated phases, including excitonic insulators, superfluids, and supersolids, potentially stable even at room temperature. When embedded in optical cavities, moir\'e excitons hybridize with photons to form moir\'e exciton-polaritons, a new class of quasiparticles exhibiting enhanced optical nonlinearities and novel topological features. In this review, we survey the theoretical foundations and experimental progress in the field of moir\'e excitons and polaritons. We begin by introducing the formation mechanisms of moir\'e patterns in two-dimensional semiconductors, and describe their impact on exciton confinement, optical selection rules, and spin-valley physics. We then discuss recent advances in the realization of many-body excitonic phases and exciton-based probes of electronic correlations. Finally, we explore the novel aspects of moir\'e polaritons, highlighting their unique nonlinear and topological properties. By bridging quantum optics, nanophotonics, and correlated electron systems, moir\'e excitons offer a powerful solid-state platform for quantum simulation, optoelectronic applications, and many-body photonics.