Raman-scattering studies of coupled modes and superconducting gap excitations in single-crystal YBa_2Cu_3O_7-δ

Abstract
The results of polarized light-scattering studies of single-crystal YBa2Cu3O7-δ are presented. In the normal state, strong electronic scattering is observed both directly and through interference effects with certain phonons. Below Tc this electronic scattering undergoes a redistribution that is due to gap formation. The redistribution of the continuum below Tc has a strong symmetry dependence, suggesting possible gap anisotropy in YBa2Cu3O7-δ. Phonon self-energy effects are also shown to be consistent with gap anisotropy. Finally, studies of untwinned single crystals illustrate striking optical anisotropy of the Raman spectra in the ab plane.