Temperature dependence of the self-field critical current densities and flux pinning in YBa2Cu3O7–δ thin films containing nanoprecipitates

Abstract

The temperature dependence of the self-field and in-field critical current densities Jc(T) was investigated in YBa2Cu3O7–δ thin films containing a high density of nanoprecipitates. The self-field Jc(T) and in-field Jc(T) were both approximated by Jc(T) ∼ (1 – T/Tc)m (1 + T/Tc)2, where the index m was mostly 2.0–2.6 in moderate magnetic fields (µ0H = 0.5–1 T, // c-axis), but m was smaller (1.5–1.8) in self-fields. This phenomenon can be explained by the assumption that the self-field Jc is determined by the flux pinning by relatively large nanoprecipitates, which is supported by simple theoretical calculations of the elementary pinning force fp due to the core pinning interaction. The self-field Jc is estimated to be proportional to 1/λ3, where λ is the penetration depth. This relationship can successfully explain the previously observed inverse correlation between the self-field Jc and the surface resistance Rs that is supposed to be proportional to λ3.