Giant Rydberg Excitons in Synthetic and Artificial Cuprous Oxide

Abstract

In this paper, we report on our recent studies of giant Rydberg excitons in cuprous oxide (Cu 2 O). Cuprous oxide exhibits an extraordinary exciton spectrum near its 2.17 eV band edge. Unlike most semiconductors, excited states with principal quantum number up to n = 25 have been observed. This contrasts with more conventional semiconductors, where it is common to observe principal quantum numbers up to n = 5. Such large principal quantum numbers imply macroscopic quantum objects that might be harnessed for a host of different quantum technology applications. Until recently, the highest principal quantum number excitons had only been observed in natural cuprite gemstone material recovered from a small number of mines in Africa. We reported cuprous oxide excitons in similar gemstone material with principal quantum numbers up to n = 15 at this conference in 2017. Recently, we have observed excitons in synthetic cuprous oxide. The single crystal material was grown by the optical float zone technique. X-ray characterisation confirms that the material is mostly single crystal. Our first optical characterisation has been promising, and we have observed excitons with similarly large principal quantum numbers seen in natural gemstone material. Our results are particularly important because they indicate a real technological pathway for this extraordinary material.