The Low-Field Ac Impedance of YBa2Cu3O7-δSuperconducting Slab

Using results of surface impedance measurements, the penetration of ac field into a melt-textured YBa 2 Cu 3 O 7-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 µ0H dc ≤ 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.