Optical properties of linear-chain mercury compounds

Abstract

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 $\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}\ensuremath{-}\stackrel{\ensuremath{\rightarrow}}{\mathrm{b}}$ plane) with free-electron Drude theory giving a satisfactory initial description of the data. The plasma frequency is found to be $\ensuremath{\hbar}{\ensuremath{\omega}}_{p}=4.8$ eV and combined with the electron density yields a free-electron optical mass. The implied optical conductivity in the $a\ensuremath{-}b$ plane at room temperature is ${\ensuremath{\sigma}}_{\mathrm{opt}}={(4\ensuremath{\pi})}^{\ensuremath{-}1}{\ensuremath{\omega}}_{p}^{2}\ensuremath{\tau}\ensuremath{\simeq}{10}^{4}$ ${(\mathrm{\ensuremath{\Omega}}\mathrm{c}\mathrm{m})}^{\ensuremath{-}1}$ in good agreement with the measured dc value. Normal-incidence studies of reflectance from crystal faces at an angle with the $a\ensuremath{-}b$ plane are analyzed to provide a complete description of the complex dielectric tensor in the spectral range from 0.5 to 4.2 eV.