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Overcoming the barrier to width superconducting coatings
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Comparison of experimental and calculated vs thickness. A simple model of an incremental critical current density that varies as a function of depth in the film provides an excellent fit (line) to the experimental data (symbols). In the model, is highest——at the interface between YBCO and the substrate or buffer layer ; it declines linearly to over a range , and remains constant thereafter. Experimental data are for single crystal substrates. All measurements in this work were carried out at in self-field, using -wide patterned bridges of length. (b) Experimental confirmation of the conceptual incremental function . The dotted line is the incremental critical current density model used for the fit in Fig. 1(a). The best fit is obtained when is adjusted to . The symbols are for three different YBCO films that have been ion milled (see Ref. 11). As each layer is milled away, the changes in both thickness and current of the remaining film are measured, allowing to be determined layer by layer.

Image of FIG. 2.
FIG. 2.

Transmission electron microscope image of a pulsed laser deposition YBCO film on a single crystal MgO substrate with a buffer layer. In this cross section a high density of defects near the YBCO- interface is visible as a dark band extending about into the YBCO, while a much lower density of threading dislocations has propagated vertically through the superconductor. Each set of defects may give rise to a different .

Image of FIG. 3.
FIG. 3.

Comparison of single-layer and YBCO/ multilayer films on electropolished alloy substrates (see Ref. 26) coated with a textured layer of MgO by ion beam assisted deposition (Ref. 27) and a buffer layer Ref. 28. As indicated by the dotted line contours—showing the combination of and thickness needed to reach a critical current of 600 or in a -wide tape—single-layer coatings do not reach width unless the thickness is more than . Four-layer multilayers, however, readily exceed this current, and six-layer multilayers can reach up to width at below thickness. The key is in the multilayers’ ability to preserve thin-film values, as indicated by the arrow. Here, six -thick YBCO layers, separated by -thick layers, have a of —nearly that of a single layer.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Overcoming the barrier to 1000A∕cm width superconducting coatings