LINEAR LOW-TEMPERATURE DEPENDENCE OF THE SURFACE IMPEDANCE OF A BA0.6K0.4BIO3 SINGLE-CRYSTAL

The temperature dependences of the real part R(s) and the imaginary pa rt X(s) of the surface impedance Z(s) = R(s) + iX(s) of the supercondu ctor Ba0.6K0.4BiO3 (Tc similar or equal to 30 K) are measured at a fre quency of 9.4 GHz. Its temperature dependence Z(s)(T) and that of the complex conductivity sigma(s)(T) can be described on the basis of a tw o-fluid model under two assumptions: The density of superconducting ca rriers increases linearly, and the relaxation time increases as a powe r law (proportional to/T-5), with decreasing temperature T<T-c. This m odel also describes well the curves Z(s)(T) and sigma(s)(T) recently m easured for YBa2Cu3O6.95 and Bi2Sr2CaCu2O8 single crystals. (C) 1996 A merican Institute of Physics.