Current percolation and theV-Itransition in YBa₂Cu₃O₇bicrystals and granular coated conductors

Abstract

There is considerable interest in the dynamics of vortices in granular `coated conductors' consisting of a 2D network of low angle grain boundaries (LAGBs). The V-I characteristic of the conductor is determined by a combination of flux vortex channelling along the grain boundaries and current percolation within the grain network. In this work it is shown that measurements of viscous flow for a YBa2Cu3O7 bicrystal LAGB can be applied in a statistical model that predicts the characteristic V-I response for a particular grain-to-grain dispersion of grain boundary angles.

Voltage–current characteristics of epitaxial and misoriented Ba(Fe1-xCoxRodriguez1, Mariño2 2015Physica C: Superconductivity and its Applications

“…At low magnetic fields (4 T in this case), a kinked V-I transitions with several linear segments and different dV=dI gradients are observed in contrast to the smoothly curve of the epitaxial films (Grain J c limitation). This behavior may be related to a vortex channeling and a viscous flow of the flux lines with a change in the number of vortex rows flowing at the grain boundary [22][23][24]. The smoothly curves in the misoriented films are observed when the granular irreversibility field has been exceeded (T = 10 K, H > 4 T).…”

Comparison of ac susceptibility of YBa2Cu3O7 coated conductors and single crystals

“…[3][4][5][6] This feature should also be reflected in ac susceptibility data of the coated conductor. In order to confirm this, we have calculated numerically the ac susceptibility of a superconducting cylinder with a V -I characteristic whose nonzero E = ͑J − J c ͒ at J Ͼ J c .…”

“…3 Systematic experimental studies have been carried out mainly on transport properties of bicrystals with specially patterned bridges for setting electric contacts. [4][5][6] For the research and development of coated conductors, it is desired to develop more convenient contactless techniques. In the present letter, we describe our ac susceptibility technique, by which the properties of any sample of coated conductors can be studied quantitatively.…”

Nanosize patterns as reference structures for macroscopic transport properties and vortex phases in YBCO films

“…In fact, a lot of studies were performed on bicrystals of various kind, because these bicrystals can offer good model systems to obtain detailed information concerning the effect of grain boundary (GB) interfaces in films. It must however be emphasized that they offer a good model for what concerns granularity appearing at a mixed nanometric-micrometric scale (nanometric for single dislocations, micrometric for larger mismatch zones [4]), while only occasionally the impact of granularities appearing at just a gauge scale (it means at a few nanometer scale) can be guessed [5]. Besides an extreme care in this respect [6,7], the studies concerning low angle grain boundaries (GB) are particularly appropriate to the matter of films.…”