Optical properties of single-crystal rutile RuO2and IrO2in the range 0.5 to 9.5 eV

We have measured the near-normal incidence reflectivity of single-crystal rutile Ru${\mathrm{O}}_2$ and Ir${\mathrm{O}}_2$ for $\overrightarrow{\mathrm{E}}\parallel c$ axis and $\overrightarrow{\mathrm{E}}\perp c$ axis at room temperature in the photon energy range 0.5-9.5 eV. From a Kramers-Kronig analysis of the reflectivity we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant (${\epsilon }_1$ and ${\epsilon }_2$, respectively) and refractive index ($n$ and $k$, respectively) for each material. Comparison with recent band-structure and density-of-states calculations and past experimental studies of related solids has enabled us to gain further insight into the nature of the oxygen $p$ electrons and metal $d$ electrons in these materials.