Breakdown of Fermi's Golden Rule in Exciton–Photon Interaction

Abstract

According to Fermi's golden rule, the radiative decay rate of excitons in a thin film becomes higher with increasing film thickness because of the increment of the interaction volume between excitons and photons. However, for a thick film, the decay rate is inversely proportional to the film thickness, because the excitons behave as polaritons and the decay time is proportional to the time of flight. This contradiction reflects a breakdown of Fermi's golden rule in the exciton–photon interaction. We have revealed the breakdown condition by a rigorous calculation method that connects the two radiative decay schemes.