An anomalous effect in the low-field ac susceptibility of Y Ba2 Cu3 O7-δ superconductors with strong frequency dependence is presented. This phenomenon appears in samples whose intergranular currents flow with low values, and its existence is analyzed in terms of the presense of Josephson vortices and their thermally activated creep of Kim-Anderson type with small pinning potential. Its existence highlights a possible problem in the research and development of high-temperature superconductors; some materials with high Jc defined by E= Ec = 10-4 Vm may still have a large resistivity at lower E. © 2005 The American Physical Society.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 1 Aug 2005|