Surface ExcitonPolariton in Cesium Lead Halide Perovskites

In this article, we developed a theory describing surface exciton polaritons (SEPs) that accounts for the spatial dispersion of the dielectric constant connected with exciton momentum. Due to strong coupling between light and bulk excitons in the frequency separation, ℏω_LT, between the longitudinal and transverse excitons, the SEP is formed and behaves as partially light and partially matter. The dispersion of the SEP was found through a combined solution of Maxwell’s and Thomas-Hopfield’s equations. The analytical theory describes SEPs at any bulk exciton/vacuum interface and provides its complete dispersion if one knows ℏω_LT, the exciton effective mass, <i>M</i>, and the high-frequency dielectric constant, κ_∞. The presented theory is in excellent agreement with the only numerical modeling of this problem, which was conducted for SEPs at a ZnO/vacuum interface. Calculations show the spatial dispersion of the dielectric constant leads to rather small broadening of the photon-like quasi-particle and suggest using SEPs for long-range coherence transfer. The theory was used to describe SEP dispersion in CsPbCl₃ and CsPbBr₃ perovskites.