Dielectric function in HgTe between 8 and 300°K

Abstract

Reflectivity spectra of HgTe were measured in the spectral region from 80 to 600 ${\mathrm{cm}}^{\ensuremath{-}1}$ at temperatures between 8 and 300\ifmmode^\circ\else\textdegree\fi{}K. The wave numbers of the transverse-optical phonon ${\ensuremath{\omega}}_{\mathrm{TO}}=117$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and longitudinal-optical phonon ${\ensuremath{\omega}}_{\mathrm{LO}}=132$ ${\mathrm{cm}}^{\ensuremath{-}1}$ at 8\ifmmode^\circ\else\textdegree\fi{}K were determined. The total dielectric function including the interband ${\ensuremath{\Gamma}}_{8}\ensuremath{-}{\ensuremath{\Gamma}}_{8}$ contribution was analyzed. Plasmon-phonon dispersion diagrams were obtained. The theoretical analysis is compared with experimental results at all temperatures. Possible consequences of the adiabatic approximation breaking down in zero-gap semiconductors is examined. A new low-frequency mode is reported, its temperature dependence is given, and its origin is discussed from physicochemical arguments.