Thermal stability of correlated defects introduced by heavy ion irradiation in YBa₂CU₃O_7-δ

We study the thermal stability of columnar defects in YBa₂Cu₃O_7-δ single crystals introduced by irradiation with 3.9 GeV Au²⁹⁺. The dependence of the critical current density on the annealing temperatures is correlated with changes in the microstructure of the defects, as seen from transmission electron microscopy measurements. We find that the defects induced by irradiation are stable upon thermal annealing up to temperatures of 600 °C and that the critical current density at temperatures T≥45 K can actually increase with thermal annealing.