MICROWAVE FREQUENCY SURFACE IMPEDANCE OF HIGH-T-C SINGLE-CRYSTALS

Currently available data on the real, R-s, and imaginary, X-s, parts o f the microwave frequency surface impedance Z(s) = R-s + iX(s) are pre sented for high quality single-crystal high-temperature superconductor s YBa2Cu3O6.95, Ba0.6K0.4BiO3, Tl2Ba2CaCu2O8-delta, Tl2Ba2CuO6+delta, and Bi2Sr2CaCu2O8. A high-precision technique for measuring the temper ature dependences R-s(T) and X-s(T) in the range 4.2 less than or equa l to T less than or equal to 150 K is described. Surface impedance and complex conductivity features common to single crystal high temperatu re superconductors are formulated and the temperature variation of the se properties is analyzed. To explain the experimental data, a modifie d two-liquid model is used, which includes quasiparticle scattering an d accounts for the characteristic change in the density of superconduc ting carriers at low at near-critical temperatures. Prospects for the microscopic theory of high frequency response of high-temperature supe rconductors is discussed.