BEHAVIOR OF THE RAMAN CONTINUUM AND RAMAN GAP IN TC = 60-K YBA2CU3O7-DELTA

Numerous Raman investigations of the 90-K phase of YBa2Cu3O7- have revealed broad features at approximately 350 and 500 cm-1 in the A1g and B1g symmetries, respectively, which exhibit behavior qualitatively similar to the gap redistribution expected of a BCS-like superconductor. We find, however, that in decreasing the oxygen concentration to achieve an untwinned Tc=60 K single crystal the gaplike features do not exhibit straightforward BCS behavior. Rather, the 500-cm-1 B1g peak is found to be insen- sitive to the change in carrier concentration and is found to persist well into the normal state while the A1g peak exhibits significant broadening and no apparent softening. In addition, we present results on the room-temperature phonons and on an anomalous response of the background continuum to incident laser power. © 1990 The American Physical Society.