Interchange of the Quantum States of Confined Excitons Caused by Radiative Corrections in CuCl Films

Abstract

The energy states of a particle confined in a narrow space are discrete and lined up in the order of n=1,2,3,.... However, if the particle interacts with a radiation field, modification of the energy, referred to radiative correction, will occur and quantum states are expected to interchange. We investigated the center-of-mass confinement of excitons in CuCl films by a new method based on "nondegenerate two-photon excitation scattering." The energies of confined excitons in a 19.3 nm thick film are found to be lined up in the order of n=1,3,5, because the radiative correction is very weak. On the other hand, in a 35.3 nm thick film, in which the radiative correction becomes large, the energies of quantum states are ordered n=2,3,4,1,5,7. This interchange is confirmed by comparing the calculated scattering spectra, in which radiative correction is taken into account, with the measured ones.

Radiative coupling of A and B excitons in ZnO

“…Accordingly, a wave-wave coupling between excitons and radiation occurs, and their interaction volume becomes considerably larger, especially for multipole-type excitons with the CM quantum number λ ≥ 2, leading to large radiative corrections. As a result, the nonlinear optical responses are enhanced [29][30][31] , and the level shift and radiative decay rate are resonantly increased [32][33][34] with the sample size. We should note that such a large interaction volume also strengthens the coupling between different components of excitons via radiation.…”

“…For example, the lowest peak with thickness 150 nm is dominantly attributed to the λ = 3 exciton of both A and B excitons, although that with thickness 220 nm is dominantly attributed to the λ = 4 exciton. This is because the large radiative corrections cause interchanges of the quantized excitonic states 32 . Second, the mixing of A and B excitons becomes significant with increase in the energy shifts from the bare exciton energies.…”

“…In previous researches, our theoretical scheme has successfully reconstructed experimental data for singlecomponent excitonic systems such as CuCl 32,34 . In the case of multicomponent excitonic system, however, the effects of radiative coupling between different excitonic branches would be expected to reflect in the nonlinear optical signals.…”

“…The real part Re[ ω ξ ] gives the eigenenergy including the radiative shift and the imaginary part −Im[ ω ξ ] gives the radiative width. An increase in the film thickness leads to a large interaction volume between excitonic waves and radiation waves, and their phase-matching leads to the large radiative correction from the bare excitonic states especially in a nano-to-bulk crossover size regime [30][31][32][33][34] .…”

Generation of entangled-photon pairs from biexcitons in CuCl thin films: Nano-to-bulk crossover regime

“…Actually, owing to the recent development of nanoscale fabrication, anomalous nonlinear optical processes have been reported in semiconductor nano-structures and in the nano-to-bulk crossover regime. 17,[26][27][28][29][30][31][32][33][34][35][36] Further, it shows a rapid radiative decay rate of excitons on the order of 100 fs due to the exciton superradiance.…”