Effects of Uniaxial Stress on Excitons in CuCl

The effects of uniaxial stress on the exciton reflection spectra of zinc-blende CuCl have been investigated experimentally and theoretically. From a comparison of the experimental results with a theory which takes account of the strain, spin-exchange, and stress-induced $k$-linear terms, it is established that the stress-induced $k$-linear term is playing an essential role in the anomalous transverse-longitudinal mode mixing of the $Z_3$ exciton observed in a configuration of $\overrightarrow{\mathrm{P}}\parallel \mathrm{}\left[001\right]\mathrm{}$ and $\overrightarrow{\mathrm{K}}\parallel \mathrm{}\left[110\right]\mathrm{}$. The coefficient of the stress-induced $k$-linear term is estimated to be about ${10}^{-7\mathrm{}}$ eV cm, which seems to be reasonable in comparison with the previously known $k$-linear term in CdS. It is further proved that this effect is closely related to a stress-induced gyrotropy in deformed CuCl from macroscopic considerations on the dielectric tensor with a spatial dispersion linear in $\overrightarrow{\mathrm{K}}$. Additional contribution of the effect of an off-axis incidence in case of lower symmetry is also discussed.