THE EFFECTIVE PENETRATION DEPTH OF A HIGH-Tc SUPERCONDUCTOR YBa₂Cu₃O₇

The dependence of the effective penetration depth λ_e, on the external magnetic field in a high-Tc superconducter YBa2Cu3O7 has been measured by both dc and ac methods at liquid-nigtrogen temperature. It is found, that λ_e increases rapidly with increasing external field and is 0.13~0.15mm in macroscopic scale. The Hcl of the specimen, about 800e at 77K here, can be determined more reliably by comparing dc λ_e with ac λ_e . The difference between λ_edc and λ_eac, and the jumping of λ_edc may indicate the characters of superconducting glass.