Splitting of the interband absorption edge in Au: Temperature dependence

The optical absorption spectra of bulk gold were measured polarimetrically at 90, 295, and 725 K in the 1.0-3.5-eV region. The experimental data have been fitted using a model calculation which accounts for the temperature-induced smearing of the Fermi surface. The optical gaps and the interband matrix elements for the $d$-bands to Fermi-surface transitions near $X$ and $L$ have been determined as a function of temperature. The present data show that the parabolic shape of the absorption edge, which has been reported to extend to 3.5 eV, is largely coincidental for photon energies above 2.65 eV. Rather a tentative analysis suggests that the transitions in the vicinity of $L$ lose their dominant importance in shaping the absorption edge above 2.65 eV.