Role of dislocations on the formation of the Abrikosov lattice in Nb superconductor

Quantized magnetic flux lines (vortices) in superconducting Nb foils were d irectly observed with various externally applied magnetic fields in a cryo- lorentz electron microscope. The interaction between vortices and dislocati ons was examined; edge-on dislocations weakly pin individual Vortices at ma gnetic fields below 100 G. In higher magnetic fields the formation of a reg ular hexagonal vortex lattice starts preferentially at in-plane dislocation s. At 200 G small domains of the Abrikosov vortex lattice is formed. Based on these observations the mechanism for the formation of the Abrikosov latt ice is proposed. (C) 1999 Published by Elsevier Science Ltd. All rights res erved.