Optical effects caused by coincidence between the energies of the plasma oscillations and the band-to-band transition in bismuth crystals doped with an acceptor impurity

The energy of plasma oscillations of free charge carriers in bismuth crystals ?ω_p can be qual to the band gap at the L point of the Brillouin zone E _gL as a result of doping with an acceptor impurity. Variation in the edge shape and splitting of the minimum in the plasma reflection are observed in experimental studies of reflection under normal incidence of radiation on the crystal. An analysis of the totality of available experimental data shows that the above special features are caused by interaction of elementary excitations (such as the plasma oscillations) with band-to-band transitions. It became possible for the first time to ascertain the composition of the bismuth crystals for which the condition ?ω_p=E _gL is satisfied and observe the variation in the characteristics of the plasma oscillations of free charge carriers, which occurs as a result of electron-plasmon interaction.