We have measured reflectance, ellipsometric, and Raman spectra on thin films of isotropic metallic oxides ${\mathrm{La}}_{0.5}$${\mathrm{Sr}}_{0.5}$${\mathrm{CoO}}_3$ and ${\mathrm{Ca}}_{0.5}$${\mathrm{Sr}}_{0.5}$${\mathrm{RuO}}_3$. The spectra strongly resemble those of cuprate superconductors. In particular, reflectance is a nearly linear function of frequency throughout the infrared, and the electronic Raman scattering continuum is nearly independent of energy. Neither of the compounds is superconducting down to 4.2 K, while their electronic excitations spectra are apparently like those of the cuprates. Hence, it seems unlikely that the corresponding "anomalous" dielectric response could be the sole root of high-temperature superconductivity.

• Received 28 May 1993

DOI:https://doi.org/10.1103/PhysRevLett.73.1436