The Low-Field Ac Impedance of YBa2Cu3O7−δ Superconducting Slab

Using results of surface impedance measurements, the penetration of ac field into a melt-textured YBa2Cu3O7−δ slab was investigated. We obtained a linear correlation between the surface impedance and ac frequency. The impedance curve shifts towards higher temperatures — 0.9 K per decade of the frequency increase, for dc magnetic field µ0Hdc ≤ 8 × 10−3 T. This is an evidence of thermally activated flux creep. A plateau in the temperature dependence of the real impedance part was observed at approximately 88 K. PACS numbers: 74.25.Qt, 74.70.Ad 1