Reproducibility of the disordered vortex structure in twinned single crystals of YBCO

Bitter decorations of the vortices in twinned single crystal YBCO have been obtained to study the disordered structure formed on successive cooldowns of the sample under the same conditions of field and temperature. Between s uccesive decorations, the iron dots could be removed completely, giving a s urface clean enough for further decoration. It was found that successive re alizations of the disordered vortex state were very similar at long range, and differed mostly on short scales, compared to the average vortex separat ion. We have quantified the correlation between successive structures, and double sided decorations have been also performed to compare with the exten t of spatial correlation in the applied field direction. The coincidence of the position of the vortices in successive realizations of the structure, is unexpected, and indicates an unusual behavior for a glassy system. Our t echnique makes it possible to image the position of the vortices in detail and repeatedly, providing us with a model amorphous system in which to stud y the reproducibility of the disordered structure.