Light Scattering from Single-Particle Excitations of Carriers in Lead Salts: Charge-Density and Spin-Density Fluctuations

In the absence of any magnetic field, Raman scattering from single-particle intraband electronic excitations in either $p$-type or $n$-type PbTe, PbSe, and PbS has been calculated. Because of the anisotropic many-valleyed Fermi surface and large spin-orbit coupling, it is shown that contributions to the scattering cross section from both charge-density fluctuations and spin-density fluctuations are large in these materials. Numerical values for coefficients occuring in the total scattering amplitude are obtained by considering the band-edge structure near the band gap at the $L$ point in the Brillouin zone. An effective interaction Hamiltonian for the scattering process has been derived. The problem of studying the energy distribution of carriers in these materials by using a C${\mathrm{O}}_2$ laser is discussed. Because of the relatively large value of the band gap, a CO laser is found to be better for PbS.