Kondo scattering and properties of TmSe in the infrared region

The conductivity and permittivity spectra of the intermediate-valence semiconductor TmSe have been measured by terahertz and infrared spectroscopy in a frequency range of 10–10⁴ cm^?1 and a temperature range of 5–300 K. At low temperatures (5 K < T < 100 K), the spectra contain a gap Δ ≈ 2.5 meV, whose appearance is considered to be related to conduction-electron localization at local magnetic moments. At high temperatures (100 K < T < 300 K), the dielectric response is specified by two electronic components: “ light” conduction electrons and “heavy” hybridized f-d states. The microscopic parameters of both components, such as the concentration, mobility, effective mass, relaxation frequency, and the plasma frequency, are determined.