Extended dislocation-based pinning mechanism in superconducting YBa2Cu3O7 films

Abstract

To describe the critical current density ͑J c ͒ as the function of applied magnetic field ͑B a ͒ in high quality YBa 2 Cu 3 O 7 ͑YBCO͒ superconducting films, the vortex pinning mechanism along the structural domain boundaries of the films is developed. The boundaries, assumed to have low misorientation angles, are quantitatively considered to consist of individual edge dislocations acting as pinning wells, rather than a continuous boundary. This extended model accurately describes the experimental J c ͑B a ͒ over the wide field and temperature ranges. Marginal deviations of the model from the experimental J c ͑B a ͒ curves are observed at high fields and temperatures where thermally activated depinning is significant. This pinning model is verified to provide precise structural properties of the films which can be obtained by other considerations.Understanding of electromagnetic behavior of YBa 2 Cu 3 O 7 ͑YBCO͒ superconducting thin films at applied magnetic field ͑B a ͒ is important task of theoretical and experimental physics. Numerous attempts 1-3 to describe pinning mechanisms resulting in high J c have led to controversial conclusions on the origin of the strong pinning in the films. The successful model 3 working over the entire B a range has been proposed on the basis of the experimental evidence 1,4,5 indicating the significant contribution of the linear defects ͑dislocations͒ to vortex pinning. Indeed, this type of defects can pin vortices along their entire length, providing the strongest available pinning. 6-8 The other successful model 9,10 is based on the only assumption of the network of Josephson junctions governing J c ͑B a ͒ dependence in YBCO films. This assumption is unlikely to be the case in the quality YBCO films with high J c having low angle boundaries between structural domains. 11 In Ref. 3, it was assumed that the vortices are effectively pinned on out-of-plane extended defects ͓edge dislocations ͑EDs͔͒, which form a network of structural domains separated by low angle boundaries ͑LABs͒. This model deals with statistical domain size distribution and the pinning width ␦ c , 12,13 which characterizes the width of pinning walls formed by LABs. Basic idea is to calculate the probability to pin vortices, which form a flux-line lattice ͑FLL͒, by trapping them within the range ␦ Յ ␦ c .Real YBCO films demonstrate not only different domain size distribution, but also different low angles between these domains. Different angles between domains imply different spacing d between the EDs, which govern J c in the films. 11 The spacing d has been qualitatively mentioned in the original model, however, the quantitative approach has not been developed.In this work, we have substantially extended the statistical model by introducing more realistic the modulated pinning landscape along LABs and the rectangular ͑rather than square͒ shape of the domains. It has allowed us to explain the behavior of J c ͑B a ͒ curves with a better accuracy in the low and intermediate B a regions. Comparison of two slightly ...

Rectifying differences in transport, dynamic, and quasi-equilibrium measurements of critical current density

“…If 2d > d, the entire domain wall acts as the pinning area because the pinning zones d around dislocations overlap. Thus, the geometrical correction for these cases is given as 49,53 …”

“…1). The ratio of the pinned vortices (n p ) to the total number of vortices (n v ), the so-called accommodation function, is given by 12,49 The accommodation function depends on the average domain size hLi via l ¼ hLi= with l and being characteristic of domain size distribution. Parameter d(B a ) is defined through the competition between vortex displacement energy in the flux line lattice (FLL) from its equilibrium position and pinning energy,…”

“…The field dependence requires considering a certain geometrical correction due to the varying shape of the pinning potential as follows. 49,53 If 2d < d (d is the distance between dislocations in a domain wall) each dislocation core in this boundary act as a single pinning centre. In this case, the probability for a vortex in the boundary zone to be pinned is the ratio of the pinning area around each dislocation pd 2 to the assumed rectangular pinning area of the boundary 2dd.…”