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.