Radiative coupling of A and B excitons in ZnO

TL;DR

This paper theoretically investigates the radiative coupling between A and B excitons in ZnO, revealing eigenmodes and excitonic component ratios, especially in nano-to-bulk size regimes, challenging conventional independent exciton models.

Contribution

It introduces a self-consistent model considering exciton center-of-mass motion and reveals exciton-radiation coupling effects in ZnO, especially in nano-to-bulk regimes.

Findings

Radiative coupling causes mixed excitonic eigenmodes.

Enhanced radiative correction in nano-to-bulk regimes.

Contrasts with conventional independent exciton models.

Abstract

Radiation-induced coupling between A and B excitons in ZnO is theoretically studied. Considering the center-of-mass motion of excitons in bulk and thin film structures, we reveal the eigenmodes of an exciton--radiation coupled system and the ratio of each excitonic component, which is determined from diagonalization of the self-consistent equation between the polarization and the Maxwell electric field. In particular, in a nano-to-bulk crossover size regime, the large interaction volume between multipole-type excitonic waves and radiation waves causes radiative coupling between excitons from different valence bands, which leads to an enhancement of the radiative correction. The results presented in this study are in striking contrast with the conventional view of the optical response of excitons in ZnO, where A and B excitons are independently assigned to their respective spectral structures. It is also clarified that the density of each excitonic component is of a significant value for attribution of nonlinear optical signals.