Surface impedance of HTSC single crystals in the microwave band
Institute of Solid State Physics, Russian Academy of Sciences, Akademika Osip'yana str. 2, Chernogolovka, Moscow Region, 142432, Russian Federation
Currently available data on the real, Rs, and imaginary, Xs, parts of the microwave frequency surface impedance Zs = Rs + i Xs are presented for the high-quality singlecrystal high-temperature superconductors YBa2Cu3O6.95, Ba0.6K0.4BiO3, Tl2Ba2CaCu2O8-δ, Tl2Ba2CuO6 + δ, and Bi2Sr2CaCu2O8. A high-precision technique for measuring the temperature dependences Rs(T) and Xs(T) in the range 4.2 \leqslant T \leqslant 150 K is described. Surface impedance and complex conductivity features common to single-crystal high-temperature superconductors are formulated and the temperature variation of these properties is analyzed. To explain the experimental data, a modified two-fluid model is used, which includes quasi-particle scattering and accounts for the characteristic change in the density of superconducting carriers at low and near-critical temperatures. Prospects for the microscopic theory of the high-frequency response of high-temperature superconductors are discussed.