Optical properties of linear-chain mercury compounds

Polarized reflectance studies from single-crystal faces of the anisotropic Hg-chain conductor ${\mathrm{Hg}}_{2.86}$ As${\mathrm{F}}_6$ are presented. The results indicate metallic behavior for electronic excitations along the chains (in the $\overrightarrow{\mathrm{a}}-\overrightarrow{\mathrm{b}}$ plane) with free-electron Drude theory giving a satisfactory initial description of the data. The plasma frequency is found to be $\hslash {\omega }_p=4.8\mathrm{}$ eV and combined with the electron density yields a free-electron optical mass. The implied optical conductivity in the $a-b$ plane at room temperature is ${\sigma }_{\mathrm{opt}}={\left(4\mathrm{}\pi \right)}^{-1\mathrm{}}{\omega }_p^2\tau \simeq {10}^4$ ${\left(\mathrm{\Omega }\mathrm{c}\mathrm{m}\right)}^{-1\mathrm{}}$ in good agreement with the measured dc value. Normal-incidence studies of reflectance from crystal faces at an angle with the $a-b$ plane are analyzed to provide a complete description of the complex dielectric tensor in the spectral range from 0.5 to 4.2 eV.