Rydberg exciton–polaritons in a Cu2O microcavity

Abstract

Giant Rydberg excitons with principal quantum numbers as high as $n=25$ have been observed in cuprous oxide (Cu$_2$O), a semiconductor where the exciton diameter can become as large as a micrometre. The giant dimension of these excitons results in excitonic interaction enhancements of orders of magnitude. Rydberg exciton-polaritons, formed by the strong coupling of Rydberg excitons to cavity photons, are a promising route to exploit these interactions and achieve a scalable, strongly correlated solid-state platform. However, the strong coupling of these excitons to cavity photons has remained elusive. Here, by embedding a thin Cu$_2$O crystal into a Fabry-Pérot microcavity, we achieve strong coupling of light to Cu$_2$O Rydberg excitons up to $n=6$ and demonstrate the formation of Cu$_2$O Rydberg exciton-polaritons. These results pave the way towards realising strongly interacting exciton-polaritons and exploring strongly correlated phases of matter using light on a chip.