High resolution bitter patterns on superconductors

Abstract

A new technique is described for replicating the distribution of magnetic flux in superconductors. The technique involves the deposition of fine ferromagnetic powders, formed by evaporation in a poor vacuum, onto the surface of the superconductor. The patterns formed by the powder replicate the distribution of magnetic flux with a resolution of the order of 400 Å. Macroscopically, the patterns are consistent with predictions arising from the Bean model and with the recent experimental data obtained by Cline, Rose and Wulff using a magneto-resistance probe. The microscopic patterns on a cold-worked specimen of niobium-25% zirconium exhibit a cellular configuration similar in size and shape to the dislocation configuration of the specimen. On an annealed specimen of the same material, the microscopic pattern replicates the distribution of a second phase precipitate and the grain structure of the specimen, while the cellular configuration is absent.