Thin films of the high-temperature superconductor YBa₂Cu₃O(7-δ) exhibit both a large critical current (the superconducting current density generally lies between 10 and 10 A m^-2 at 4.2 K in zero magnetic field) and a decrease in such currents with magnetic field that point to the importance of strong vortex pinning along extended defects. But it has hitherto been unclear which types of defect - dislocations, grain boundaries, surface corrugations and anti-phase boundaries - are responsible. Here we make use of a sequential etching technique to address this question. We find that both edge and screw dislocations, which can be mapped quantitatively by this technique, are the linear defects that provide the strong pinning centres responsible for the high critical currents observed in these thin films. Moreover, we find that the superconducting current density is essentially independent of the density of linear defects at low magnetic fields. These natural linear defects, in contrast to artificially generated columnar defects, exhibit self-organized short-range order, suggesting that YBa₂Cu₃O(7-δ) thin films offer an attractive system for investigating the properties of vortex matter in a superconductor with a tailored defect structure.

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To investigate the quantum tunneling of almost macroscopic vortex segments we measured the normalized relaxation rate Q of superconducting currents for various high- Tc superconductors (HTS’s) down to 100 mK in magnetic fields up to 7 T. At fields below ?0.5 T, Q is essentially independent of T in the temperature regime between thermally activated and quantum motion as theoretically expected. However, at higher fields, we find an unexpected linear T dependence of Q persisting down to the lowest temperatures in all investigated samples. Since these compounds were chosen to represent the distinct classes of dirty and clean HTS’s, the extrapolated Q(T=0) values are used to discuss the theoretical models for quantum creep in the clean and dirty limits. Based on this discussion we propose a semiempirical interpolation formula for Q(T=0) which is also valid for compounds in between the dirty and clean limits.@en

Epitaxial YBa2Cu3O7-δ films nucleate in c-axis oriented single-crystalline islands. The surface of the single-crystalline SrTiO3 substrates exhibit steps of one third of the YBa2Cu3O7-δ c-axis. These steps generate a mismatch in the island boundaries between the CuO2 superconducting blocks. We show that these defect regions are strong candidates for being the pinning centers responsible for the large critical currents observed in Laser Ablated and Sputtered thin films.@en

Orientation dependent measurements of torque hysteresis loops on high quality laser-ablated YBa2Cu3O7-δ thin films were performed at a temperature of 30 K in magnetic fields up to 7 T. From these measurement we extract the field and orientation dependence of the in-plane critical current density Js(H,θ), where θ is the angle between the applied external magnetic field H and the plane of the film. Following the scaling arguments of Blatter, Geshkenbein and Larkin based on the anisotropic Ginzburg-Landau theory, we have been able to scale the measured Js(H, θ) into a form ∫(ε{lunate}(θ)H), where ε{lunate} (θ) = (sin2 θ + cos2 θ/gg2) 1 2 with γ = 3.4±0.3. The obtained value of the anisotropy parameter γ is much smaller than the values reported earlier for single crystals close to Tc.@en