TEMPERATURE-DEPENDENCE OF SURFACE IMPEDANCE OF TL2BA2CACU2O8-DELTA AND YBA2CU3O6.95 SINGLE-CRYSTALS MEASURED IN THE MICROWAVE BAND

The real part R-s and the imaginary part X-s of the surface impedance Z(s)=R-s+iX(s) of Tl2Ba2CaCu2O8-delta and YBa2Cu3O6.95 Single crystals have been measured with high precision at frequency omega/2 pi=9.4 GH z in the temperature range 0<T<140 K. In the Tl2Ba2CaCu2O8-delta cryst al a linear temperature dependence R-s(T) has been found for T less th an or equal to 50 K, and the magnetic field penetration depth lambda(4 .2 K)=X-s(4.2 K)omega mu(0) approximate to 3760 Angstrom has been meas ured. Along with well known features of the function Z(s)(T) in high-q uality YBa(2)Cu3O(6.95) Single crystals, such as the linearity of X(T) and R-s(T) for T<T-c/3 and a maximum of R-s(T) at T-T-c/2, the linear ity range of lambda(T) extends to T similar or equal to 50 K, and this curve has a plateau in the range 60<T<85 K. The curve of R-s(T) in bo th the superconducting and normal states of YBa2Cu3O6.95 is well descr ibed by a two-fluid model with the electron-phonon mechanism of quasip article relaxation. A formula describing the curve of lambda(2)(0)/lam bda(2)(T) throughout the studied temperature range is also given. (C) 1997 American Institute of Physics. [S1063-7761(97)02112-4].