Electron–Plasmon Interaction in Bi₂Te₃–Sb₂Te₃ Crystals

Upon studying the optical properties of solid solutions of p-type Bi₂Te₃–Sb₂Te₃ in the infrared range, it is found that in the single crystal Bi_0.6Sb_1.4Te₃, deformation of the reflection-coefficient spectra is observed in the frequency range of observation of the plasma resonance of free charge carriers. Deformation of the plasma edge increases with a decrease in temperature. Using the Kramers–Kronig dispersion relations from experimental reflection spectra, the spectral dependences of the real ε₁ and imaginary parts ε₂ of the permittivity function, as well as the energy-loss function characterizing the rate of energy dissipation, are calculated. Splitting of the peak of the energy loss function is found, which indicates the effect on the plasma resonance from another process occurring in the electronic system. It is established that such a process is the transition of electrons between nonequivalent extrema of the valence band. Convergence of the collective and single-particle energies of the electronic system leads to amplification of the electron—plasmon interaction, which is the most probable cause of the observed deformation of the plasma edge.