Gap anisotropy and phonon self-energy effects in single-crystal YBa2Cu3O7-

We report a Raman scattering investigation of superconducting gap anisotropy in single-crystal YBa2Cu3O7. Gap anisotropy is investigated by studying the peak in the low-temperature Raman continuum in various symmetries. Roughly a 35% difference in the energy of this peak is observed between different symmetries, suggesting the presence of substantial gap anisotropy. Anisotropy is further evidenced by the damping behavior of the 340-cm-1 Raman-active phonon below Tc, which displays increased attenuation due to phonon-induced pair breaking. The temperature dependence of this attenuation is consistent with a T=0 pair-breaking peak which is much larger than the 340-cm-1 phonon in certain regions of the Fermi surface.