TEMPERATURE DEPENDENCE OF MICROWAVE SURFACE IMPEDANCE IN YBaCuO, TlBaCaCuO, AND BaKBiO SINGLE CRYSTALS: FEATURES AND COMMON PROPERTIES

Abstract

Measurements of surface impedance Z s( T)= R s( T)+i X s( T) of YBa 2Cu 3O 6.95 (YBCO), Tl 2Ba 2CaCu 2O 8− δ (TBCCO) and Ba 0.6K 0.4BiO 3 (BKBO) single crystals versus temperature in the range 4.2≤ T≤140 K are given. The common features of all crystals under investigation are a linear temperature dependence Z s( T)∝ 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)∝ T in BKBO and TBCO takes place in the range up to T c/2, whereas in YBCO there is a broad maximum of R s( T) in the intermediate temperature range and a plateau on the curve of X s( T). The experimental data are adequately described by the two-fluid model taking into account scattering of quasiparticles and characteristic changes in the density of superconducting carriers at low temperatures and near the critical temperature.