Dielectric function in HgTe between 8 and 300°K

Reflectivity spectra of HgTe were measured in the spectral region from 80 to 600 ${\mathrm{cm}}^{-1\mathrm{}}$ at temperatures between 8 and 300°K. The wave numbers of the transverse-optical phonon ${\omega }_{\mathrm{TO}}=117\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and longitudinal-optical phonon ${\omega }_{\mathrm{LO}}=132\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ at 8°K were determined. The total dielectric function including the interband ${\Gamma }_8-{\Gamma }_8$ 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.