Deformation Potentials for Excitons in Cuprous Halides

The hydrostatic-pressure shifts of the $Z_{1,2}$ and $Z_3$ exciton peaks were measured in thin films of cubic CuCl, CuBr, and CuI at 90 K. That of the $E_1$ peak in CuI also was measured. The deformation potentials of all $Z$ excitons and of the $E_1$ exciton in CuI, about -1 eV, are more than twice those of the $Z$ excitons in CuCl and CuBr. This suggests the two valence bands in CuI may be considerably more mixed than in CuCl and CuBr.