Reproducible Nucleation Sites for Flux Dendrites in MgB2

Magneto-optical imaging was used to study dendritic flux penetration in films of MgB2. By repeating experiments under the same external conditions, reproducible features were seen in the pattern formation; dendrites tend to nucleate from fixed locations along the edge. However, their detailed structure deeper inside the film is never reproduced. The reproducibility in nucleation sites is explained as a result of edge roughness causing field hot spots.