Sensitive measurement of the surface impedance of superconducting single crystals using a sapphire dielectric resonator

A highly sensitive system based on a sapphire dielectric resonator has been developed to investigate the microwave properties of superconducting single crystals. The resonator is fabricated from a machined piece of single crystal sapphire, with a hole bored along its axis to accommodate samples. Samples are mounted on a independently heated sapphire rod, which is inserted into the region of high microwave field at the centre of the resonator. Crystals can be mounted with either their c-axis or ab-planes parallel to the microwave field. In the former configuration the predicted smallest detectable change in surface resistance is /spl sim/2.6/spl times/10/sup -4/ /spl Omega/ and is /spl sim/3.7/spl times/10/sup -4/ /spl Omega/ for the latter. Microwave measurements at 10 GHz on high quality YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// single crystals demonstrate the potential of the system for measuring the surface impedance as a function of field (up to 1.75 T parallel and 0.18 T perpendicular to microwave field) and temperature.