Microwave penetration depth measurement for high T_c superconductors by dielectric resonators

The penetration depth λ(T) dependence on temperatures for high T_c superconducting YBa₂Cu₃O_7-δ thin films stored in various environments was measured by a well-designed microwave dielectric resonator. A d-wave T² dependence was observed at low temperatures, while an exponential dependence of the penetration depth λ(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.