Abstract
Raman scattering spectra have been investigated in twin-free single crystals with various oxygen content. Superconductivity-induced effects are found for all phonons in the overdoped crystals, but they rapidly weaken with reducing oxygen content. The 340 phonon line is analyzed in detail by means of the Green function, as well as the standard Fano formula. The results provide much evidence for the nodal structure of a superconducting gap. The polarization dependence, which is significant in the highly doped crystals, illustrates the x-y anisotropy of the electronic response and implies a difference of the superconducting gap amplitudes in the and directions in the two-dimensional Brillouin zone for orthorhombic The gap energy difference decreases as the doping level is deduced.
- Received 6 December 1999
DOI:https://doi.org/10.1103/PhysRevB.61.12412
©2000 American Physical Society