Temperature dependence of the dielectric function of thin film CuI in the spectral range (0.6–8.3) eV

We determined the dielectric function of CuI by means of spectroscopic ellipsometry in the spectral range from 0.6 eV up to 8.3 eV for temperatures from 10 K to 300 K. Features observed in the dielectric function are attributed to electronic transitions in the Brillouin zone. The observed spin-orbit splitting of the top valence band of 630 meV at the Γ-point and 330 meV at the L-point are in good agreement with theoretical band structure calculations. From the temperature evolution of the critical point energies, we deduced the electron-phonon coupling constants as well as the typical phonon energies. The electron-phonon coupling for the lowest transitions at the Γ-point is found to be smaller than for high energy transitions at other symmetry points in the Brillouin zone.