Calculation of the normal state intraband electronic Raman scattering cross-section and the dielectric tensor in YBCO

Abstract

The intraband electronic Raman scattering cross-section from charge-density fluctuations of holes in YBCO has been calculated, along with their longitudinal and transverse dielectric response functions. A consistent set of electronic parameters for a simple anisotropic model of the single-particle hole energy and the normal-state collision frequency ω_c(ω,T) has been chosen in a way that leads to the observed DC and optical conductivities. Because the band-width, 2t₃, perpendicular to the a-b plane is much smaller than the Fermi energy μ in such a layered material, the Fermi surface is assumed to be open in the k_z-direction. It is taken to be almost circular in the k_x-k_y plane, but the nonparabolicity of the band is retained while calculating the unscreened part of the single-particle scattering cross-section. We show that it is possible to obtain a flat electronic Raman spectrum due to highly damped plasmon excitations, only in the extreme collision-dominated regime. Within the same model, the nature of the transverse and longitudinal dielectric tensors, and the form of the electronic part of the attractive dynamic pairing interaction, (4πe²/q²) [(1/ε(q, ω))-1], beyond the repulsive static Coulomb interaction, are also discussed.