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

The low-frequency (omega less-than-or-equal-to 1200 cm-1) Raman contin ua of YBa2Cu3Ox single crystals have been measured in both the A1g and B1g scattering geometries. The A1g continuum is found to be independe nt of oxygen concentration x for 6.93 < x < 7.00, but the spectral dis tribution in the B1g continuum depends sensitively on x in this same r egion. The spectra were also calculated by assuming that the Raman con tinua arise predominantly from scattering from the electronic excitati ons in the copper-oxygen planes, and that the band structure for the p lanes is reasonably reproduced by a two-dimensional tight-binding mode l. If a superconducting gap function with d-wave symmetry is adopted, the calculated results for A1g symmetry are found to be in good agreem ent 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 sour ces, for example scattering from spin fluctuations, that contributed t o the B1g continuum.