Temperature dependence of the critical current in high-Tc superconductors with low-angle boundaries between crystalline blocks

Abstract

A model for the limiting of the critical current in rather perfect high-Tc superconducting crystals and epitaxial films with a block structure with small angles of misorientation θ of the crystalline blocks is considered for the case when the distance d between edge dislocations along the boundary between blocks is greater than the coherence length ξ(T). It is shown that under these conditions the transparency of low-angle boundaries for the superconducting current carriers near the critical temperature Tc is practically independent of θ and T. As a result, the only factor governing the temperature dependence of the critical current density jc(T) remains the depairing current j0(T)∝(1−T/Tc)3/2. Near Tc, when ξ(T)>d, a transition from the dependence jc(T)∼(1−T/Tc)3/2 to a dependence jc(T)∼(1−T/Tc)2 occurs. This behavior of jc(T) is in good agreement with the results of experimental measurements of the critical currents in thin epitaxial films of YBa2Cu3O7−δ.

Mechanisms of limitation and nature of field dependence of critical current in HTS epitaxial YBaCUO films

“…-axis-oriented single-crystalline YBa Cu O (YBCO) films exhibit critical current densities, , two orders of magnitude higher than any kind of bulk samples [1]- [4]. The reason is supposed to be a high density of extended natural linear crystal defects.…”

“…The reason is supposed to be a high density of extended natural linear crystal defects. It is shown that two alternative mechanisms [4] of -limitation can occur in YBCO films with the highest critical current density, K A/cm . They are the depairing/ transparency mechanism and the depinning mechanism.…”

“…They are the depairing/ transparency mechanism and the depinning mechanism. Which one of these mechanisms would be realized, depends on the values of and : the lower defines the acting mechanism [4]. and are in turn determined by the film mosaic domain structure.…”

“…Out-of-plane edge dislocations are shown to play a crucial role in -behavior [6]. Peculiarities of are found in the low field range [4].…”

Depairing critical currents and self-magnetic field effects in submicron YBa2Cu3O7−δ microbridges and bicrystal junctions

“…It is worthwhile also to mention here that a theory [10] considering the critical current of wide HTS epitaxial films with small-angle misorientation between grains predicts that the j c (T) dependence is governed by the temperature dependence (1--T/T c ) 3/2 of the depairing current if the distance between edge dislocations r d on the bicrystal grain boundary is less than coherence length x (T). For a 4°g rain boundary the value of r d is equal to 5.7 nm.…”