RAMAN INVESTIGATION OF THE YBA2CU3O7 IMAGINARY RESPONSE FUNCTION

Results on the temperature dependence of the imaginary component of the response function R"(omega) in an untwinned T(c) approximately 90 K Y-Ba-Cu-O crystal are presented. We find that the normal-state imaginary parts of the response functions for the distinct A1g and B1g symmetries exhibit behavior characteristic of a quasielastic-scattering mechanism, having a temperature- and frequency-dependent relaxation rate. Further, the zero-frequency resistivities for the two symmetries inferred from this quasielastic model closely resemble the measured resistivity for single crystals of this material. Finally, a low-energy linearity of the B1g imaginary response function, accurately described in the normal state by this model in the limit omega < T, is found to persist in the superconducting state but an analysis of the slope reveals a dramatic alteration at T(c).