DIRECT OBSERVATION OF VORTEX PINNING BY DISLOCATIONS IN BI2SR2CACU2O8SINGLE-CRYSTALS

A technique allowing simultaneous observation of vortex images and cry stal defects in superconductors by transmission electron microscopy (T EM) has been developed. The vortices are visualized by the Bitter deco ration method followed by preparation of the samples for TEM. The tech nique was used to study the effect of crystal dislocations on the flux line lattice (FLL) in single crystals of Bi2Sr2CaCu2O8. Individual di slocations having a local density comparable with that of the vortices are found to cause local disorder in the otherwise well-ordered FLL, acting as attractive pinning centres. We show that the main contributi on to pinning in our experiments comes from strain fields around dislo cations. Relevant pinning mechanisms are discussed such as those arisi ng from local changes of superconducting parameters caused by the disl ocation strain fields or from vortex-dislocation interaction of an ela stic nature.