Critical current density and dynamical relaxation rate below the matching field in thin films of YBa2Cu3O7-δ

Abstract

We studied the superconducting current density j s (B, T) and dynamical relaxation rate Q(B, T) of laser ablated thin films of YBa 2 Cu 3 O 7−δ with various dislocation densities (n disl ∼ 7-70 μm −2 ). In these films dislocations act as strong pinning centers like columnar defects in heavy ion-irradiated crystals. The matching field clearly manifests itself in a constant j s (B) ∼ 5·10 11 - 1·10 12 Am −2 at T = 4.2 K and μ 0 H ≲ 0.7 B Φ and a constant Q(B). In contrast to irradiated crystals, in films we do not observe a peak in the relaxation rate Q versus T below the matching field B Φ ≡ n disl ·Φ 0 . Instead, in thin films Q(T) increases monotonously with increasing temperature. We conclude that the influence of vortex-vortex interactions in thin films is greatly reduced due to the non-random distribution of pinning sites and the low matching field.