Optical spectroscopy and electronic structure of the GdCu$_x$ compounds ($x$ = 1, 2, 5)

Optical properties of the GdCu, GdCu$_2$ and GdCu$_5$ compounds with various crystal lattices have been investigated using ellipsometry in a spectral range of 0.22–16 $\mu$m. Theoretical calculations of the electronic structure of these intermetallic compounds have been performed in the approximation of local electron density with the correction for strong electron correlations in a 4$f$ shell of gadolinium ions. Based on the results of calculations, the interpretation of experimental spectra of interband optical conductivity has been proposed. The plasma and relaxation frequencies of conduction electrons have been determined.