We describe a tunable electron paramagnetic resonance (EPR) spectrometer designed to operate at frequencies between 160 and 525 GHz and magnetic fields of up to 20 T. To operate in such a broad frequency range we use a very stable optically pumped far infrared laser. The performance of the spectrometer has been measured with solid and liquid samples. This allows us to outline the potential uses of the spectrometer.
Reflectivity spectra of HgTe were measured in the spectral region from 80 to 600 cm"' at temperatures between 8 and 300'K. The wave numbers of the transverse-optical phonon uT =117 cm ' and longitudinal-optical phonon &zo=132 cm ' at S 'K were determined. The total dielectric function including the interband Fa-I'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.
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