Surface impedance of HTSC single crystals in the microwave band
Institute of Solid-State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region, 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.