Flux pinning by symmetrical grain boundaries in niobium bicrystals

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Abstract
Flux pinning by grain boundaries has been studied using resistive measurements in a set of niobium bicrystals with defined symmetrical tilt boundaries. The results are consistent with the notion that the pinning force f p arises from a local change in the upper critical field H c2 and the Ginzburg—Landau parameter K at the boundary layer via the electron-scattering interaction. The experimental results are in good agreement with the calculations of DasGupta et al. both in terms of the magnetic field dependence and the magnitude of f p. It is found that the pinning force is dependent upon the orientation of the tilt axis, but is insensitive to the grain-boundary misorientation.