Surface excitations in metals: Brillouin and Raman light scattering

The theory of inelastic light scattering in anisotropic metals by conduction electrons interacting with acoustic and optical phonons and impurities is developed. The effects of a surface are studied in detail. The Coulomb interaction of carriers is included in a self-consistent way. The scattering cross section is evaluated. The skin effect, as well as the electron-phonon interaction, modifies the electron-hole contribution. In particular, the wide relaxation continuum obtained by Zawadowski and Cardona appears with a temperature-dependent relaxation time. Sharp peaks in the cross section arise from the excitation of bulk and surface phonons. The contribution of the mixed phonon excitations, which are a superposition of longitudinal waves diminishing from the surface into the bulk and nondiminishing transverse waves, has the form of a narrow continuum. The slipping nondiminishing longitudinal phonon produces a strong nonsymmetric maximum at the threshold of the density of states.