Two-dimensional semiconductors in the regime of strong light-matter coupling

The optical properties of transition metal dichalcogenide monolayers are widely dominated by excitons, Coulomb-bound electron–hole pairs. These quasi-particles exhibit giant oscillator strength and give rise to narrow-band, well-pronounced optical transitions, which can be brought into resonance with electromagnetic fields in microcavities and plasmonic nanostructures. Due to the atomic thinness and robustness of the monolayers, their integration in van der Waals heterostructures provides unique opportunities for engineering strong light-matter coupling. We review first results in this emerging field and outline future opportunities and challenges. Excitons, quasi-particles of tightly bound electron-hole pairs, dominate the optical response of atomically thin transition metal dichalcogenides. Here, the authors review strong light-matter coupling in two-dimensional semiconductors arising from confined excitons interacting with trapped photons or localized plasmons.