Normal-state electronic Raman-scattering efficiencies of YBa2Cu3O7-, Bi2Sr2CaCu2O8, and Tl2Ba2Ca2Cu3O10: Effects of local-density-approximation Fermi-surface mass fluctuations

Abstract

Absolute electronic Raman-continuum cross sections have been measured for orthorhombic single-domain Y-123 and Bi-2212 crystals and a tetragonal Tl-2223 film on a MgO substrate (Tc=120 K) in different polarization geometries. They agree well with effective mass fluctuations obtained for Y-123 from Fermi-surface averages of the dispersion calculated from the full-potential linear muffin-tin orbital band structure of Andersen et al. The results suggest that anisotropic mass density fluctuations involving various sheets and regions of the Fermi surface are indeed responsible for the electronic Raman continuum and predictable with realistic local-density-approximation band-structure calculations. Decomposition into contributions from the four sheets of the Fermi surface permits separation of interband and intraband mass fluctuations. Anisotropies corresponding to the orthorhombicity and the purely tetragonal A1g, B1g, and B2g symmetries are determined for the three superconductors. © 1995 The American Physical Society.