Plasmon-enhanced quadrupole transitions of Rydberg excitons in Cu2O

A mechanism for amplification of weak quadrupole transitions of Rydberg excitons in Cu$_2$O by a plasmonic nanostructure is investigated. The theoretical description of exciton-plasmon interaction is presented and a field averaging approximation is proposed for calculations involving large excitons. Various types of copper, silver and gold-based plasmonic nanostructures are considered and their potential for enhancing quadrupole transitions is evaluated.