MICROWAVE SURFACE IMPEDANCE MEASUREMENTS ON HIGH-T-C SUPERCONDUCTORS

We present measurements of the surface impedance of YBa2Cu3O7-delta an d Bi2Sr2CaCu2O8+y thin films in the TIIz regime. Below T-c, peaks in t he real part of the conductivity are observed in both materials, but d iffer in the temperature dependence. Investigations of Pr-doped YBCO r eveal deviations from the T-linear behavior of the resistivity at char acteristic temperatures that shift with the doping level and can be id entified with the occurrence of a spin gap. The spin-gap temperature a nd T-c as a function of doping span a Nagaosa-Lee-type phase diagram i n the underdoped regime.