Microwave penetration depth measurement for high T/sub c/ superconductors by dielectric resonators

Abstract

The penetration depth /spl lambda/(T) dependence on temperatures for high T/sub c/ superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films stored in various environments was measured by a well-designed microwave dielectric resonator. A d-wave T/sup 2/ dependence was observed at low temperatures, while an exponential dependence of the penetration depth /spl lambda/(T) relevant to the s wave was detected as temperature increases due to thermal fluctuation. An abnormal upturn of the penetration depth at temperatures below 10 K attributed to the surface current carried by the defect surface-induced Andreev bound states can be apparently observed without applying heavy-ion bombardment from this relatively higher frequency measurement. Readers who endeavor to start this kind of measurement can use the well-modified dielectric cavity in conjunction with the detailed measuring procedure.