INPLANE MICROWAVE CONDUCTIVITY AND QUASI-PARTICLE SCATTERING RATE OF SUPERCONDUCTING HIGH-T-C CUPRATES

The surface impedance Z(s) = R(s) + iX(s) at 9.6 and 51 GHz was measur ed in single crystals of YBa2Cu3O7, Bi2Sr2CaCu2O8, and La1.85Sr0.15CuO 4. At low temperatures, the surface resistance R(s) of all the materia ls changes linearly in temperature, and the surface reactance (penetra tion depth) also changes linearly in YBa2Cu3O7 and Bi2Sr2CaCu2O8. From Z(s) data, the complex conductivity sigma = sigma(1) - i sigma(2) and the quasiparticle scattering rate 1/tau were determined. The broad pe ak-like structure in the temperature dependence of sigma(1), which com es from strong suppression of 1/tau below T-c, is observed for all the superconductors. The low-temperature scattering rate extracted using the generalized two-fluid model is compared with the published data at different frequencies in YBa2Cu3O7. It is found that the inelastic sc attering rate 1/tau at low temperatures strongly depends on the measur ement frequency f within this model. In the microwave region, the norm alized scattering rate tau(n)/tau is nearly proportional to the normal ized frequency f/T-c, and this relation seems to be universal for opti mum-doped high-T-c superconductors. The implications for the nature of the superconducting state are discussed.