1. Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433-7919, USA
2. Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA

Correspondence to: T. Haugan¹ Correspondence and requests for materials should be addressed to T.J.H. (Email: timothy.haugan@wpafb.af.mil).

Abstract

Following the discovery of type-II high-temperature superconductors in 1986 (refs 1, 2), work has proceeded to develop these materials for power applications. One of the problems, however, has been that magnetic flux is not completely expelled, but rather is contained within magnetic fluxons, whose motion prevents larger supercurrents. It is known that the critical current of these materials can be enhanced by incorporating a high density of extended defects to act as pinning centres for the fluxons^{3, 4}. YBa₂Cu₃O₇ (YBCO or 123) is the most promising material for such applications at higher temperatures (liquid nitrogen)^{3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}. Pinning is optimized when the size of the defects approaches the superconducting coherence length ( 2–4 nm for YBCO at temperatures 77 K) and when the areal number density of defects is of the order of (H/2) 10¹¹ cm^-2, where H is the applied magnetic field in tesla^{3, 4}. Such a high density has been difficult to achieve by material-processing methods that maintain a nanosize defect, except through irradiation⁵. Here we report a method for achieving a dispersion of 8-nm-sized nanoparticles in YBCO with a high number density, which increases the critical current (at 77 K) by a factor of two to three for high magnetic fields.

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