MICROWAVE COMPLEX CONDUCTIVITY IN SINGLE-CRYSTALS OF YBA2CU3O7 AND BI2SR2CACU2OY

We measured both the surface resistance and the surface reactance at 10 GHz as functions of temperature with high precision in single crystals of YBa2Cu3O7 and Bi2Sr2CaCu2Oy in order to elucidate the confusing situation of the electromagnetic response of high-T(c) cuprates. From these measurements, we can determine the temperature dependence of the complex conductivity sigma1 - isigma2 accurately, without making special assumptions on the temperature dependence of the penetration depth. We found the common features in sigma1 (T) of both materials; sigma1 (T) has a narrow peak just below T(c) and a broad structure at low temperatures. The narrow peak is likely to be extrinsic, while the broad structure reflects an intrinsic property, i.e., the strong suppression of the quasiparticle scattering rate 1/tau. Our results imply that the strong temperature dependence of 1/tau below T(c), which behaves according to AT6 + B or C exp(T/T0) + B with B approximately omega, is a common feature of high-T(c) cuprates.