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Reconstruction of Current Flow and Imaging of Current-Limiting Defects in Polycrystalline Superconducting Films
Pashitski1, Gurevich, Polyanskii
1A. E. Pashitski, A. Gurevich, A. A. Polyanskii, D. C. Larbalestier, Applied Superconductivity Center, University of Wisconsin, Madison, WI 53706, USA. A. Goyal, E. D. Specht, D. M. Kroeger, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. J. A. DeLuca and J. E. Tkaczyk, General Electric, Schenectady, NY 12301, USA.
Abstract:
Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa2Ca2Cu3Ox films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a- and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density Jc varies widely, being up to 10 times as great as the transport Jc (scale of approximately 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport Jc is largely determined by a few high-angle boundaries.