Microwave measurement of temperature and current dependences of surface impedance for high-T/sub c/ superconductors

Abstract

Perturbation formulas for TE/sub 011/-mode dielectric rod resonator and for a TE/sub 011/-mode circular cavity resonator are derived to determine the surface impedance Z/sub s/ of superconductors from measured values of resonant frequencies and unloaded Q. The relation between the maximum surface current density of a superconductor, J/sub s/, and output power from a signal generator is derived. On the basis of these analytical results, a measurement technique is proposed to evaluate the temperature and J/sub s/ dependencies of Z/sub s/ for superconductors. The measured results of the temperature dependence of Z/sub s/ for YBCO and copper plates are presented. From these results, it is verified that the dielectric resonator is suitable for measuring the surface reactance for YBCO. From these Z/sub s/ values the temperature dependences of the skin depth and the penetration depth and those of the complex conductivity are obtained on the basis of the two-fluid model. These measured values agree well with the theoretical curves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>