LARGE EFFECT OF COLUMNAR DEFECTS ON THE THERMODYNAMIC PROPERTIES OF BI2SR2CACU2O8 SINGLE-CRYSTALS

The introduction of columnar defects by irradiation with 5.8-GeV Pb io ns is shown to affect significantly the reversible magnetic properties of Bi2Sr2CaCu2O8+gamma single crystals. Notably, the suppression of s uperconducting fluctuations on length scales greater than the separati on between columns leads to the disappearance of the ''crossing point' ' in the critical fluctuation regime. At lower temperatures, the stron g modification of the vortex energy due to pinning leads to an importa nt change of the reversible magnetization. The analysis of the latter permits the direct determination of the pinning energy.