LOW-ENERGY RAMAN CONTINUA OF YBA2CU3OX TIGHT-BINDING MODEL IMPLICATIONS

The low-frequency (omega less-than-or-equal-to 1200 cm-1) Raman continua of YBa2Cu3Ox single crystals have been measured in both the A1g and B1g scattering geometries. The A1g continuum is found to be independent of oxygen concentration x for 6.93 < x < 7.00, but the spectral distribution in the B1g continuum depends sensitively on x in this same region. The spectra were also calculated by assuming that the Raman continua arise predominantly from scattering from the electronic excitations in the copper-oxygen planes, and that the band structure for the planes is reasonably reproduced by a two-dimensional tight-binding model. If a superconducting gap function with d-wave symmetry is adopted, the calculated results for A1g symmetry are found to be in good agreement with the measured A1g spectrum. In contrast, however, the spectrum calculated in B1g symmetry is inconsistent with the observed spectral distribution. It is thus suggested that there must be additional sources, for example scattering from spin fluctuations, that contributed to the B1g continuum.