Evidence for a Dielectric Singularity in HgSe and HgTe

New experimental data on the low-temperature mobility of n-type HgSe in the concentration range 2×{}10¹⁷-5×{}10¹⁸ cm^-3 are compared with a random-phase-approximation (RPA) calculation and a concentration-independent dielectric-constant calculation. The effects of band nonparabolicity and the p-like nature of the conduction-band wave function on the scattering calculation are included. The RPA calculation is in excellent agreement with the data, while the results of the concentration-independent dielectric-constant calculation are much too low. New experimental data on HgTe in the concentration range 1.6×{}10¹⁵-4×{}10¹⁸ cm^-3 are also examined. At 1.6×{}10¹⁵ cm^-3, the RPA calculation agrees exactly with experiment, while the concentration-independent dielectric-constant calculation is too low by a factor of 3. In contrast to the case of grey tin, these results strongly support the RPA and hence the dielectric singularity predicted for symmetry-induced zero-gap semiconductors.