Rydberg excitons in synthetic cuprous oxide Cu 2 O

High-lying Rydberg states of Mott-Wannier excitons are receiving considerable interest due to the possibility of adding long-range interactions to the physics of excitons. Here, we study Rydberg excitation in bulk synthetic cuprous oxide grown by the optical float zone technique and compare the result with natural samples. X-ray characterization confirms both materials are mostly single crystal, and midinfrared transmission spectroscopy revealed little difference between synthetic and natural material. The synthetic samples show principal quantum numbers up to $n=10$, exhibit additional absorption lines, plus enhanced spatial broadening and spatial inhomogeneity. Room temperature and cryogenic photoluminescence measurements reveal a significant quantity of copper vacancies in the synthetic material. These measurements provide a route towards achieving high-$n$ excitons in synthetic crystals, opening a route to scalable quantum devices.