Recoupling Vortices due to Columnar Defects in 3.5 GeV Xe-Irradiated QMG-YBCO

摘要

Pinning properties are studied for high-energy heavy ion irradiated quenched melt growth (QMG) YBCO bulk sample. No significant enhancement of critical current densities is observed. Long-term decays of magnetizations, however, show drastic change. The magnetizations become smaller monotonically as the temperatures increase for unirradiated sample in all magnetic field range below 9 tesla. On the other hand, the temperatures recover their absolute values around 50 K for the irradiated one. This phenomenon must be originated to columnar defects introduced with the irradiation. This suggests that change of pinning host from inclusions to columnar defects occur suddenly at 50K. Recoupling (or recovery of correlation) along c-axis of vortex occurs with the aid of the columnar defects.