Temperature dependence of microwave surface impedance in YBaCuO, TlBaCaCuO, and BaKBiO single crystals: Features and common properties

Measurements of surface impedance Z(s)(T) = R-s(T) + iX(s)(T) of YBa2Cu3O6. 95 (YBCO), Tl2Ba2CaCu2O8-delta (TBCCO) and Ba0.6K0.4BiO3 (BKBO) single crys tals versus temperature are given. The common features of all crystals unde r investigation are a linear temperature dependence Z(s)(T) proportional to T at low temperatures T << T-c and an abrupt increase in Z(s)(T) as T --> T-c. The linear dependence Z(s)(T) proportional to T in BKBO and TBCO takes place in the range up to T-c/2, whereas in YBCO there is a broad maximum o f R-s(T) in the intermediate temperature range and a plateau on the curve o f X-s(T). The experimental data are adequately described by the modified tw o-fluid model taking into account scattering of quasiparticles and characte ristic changes in the density of superconducting carriers at low temperatur es and near the critical temperature. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.