COLUMNAR DEFECTS INDUCED BY HIGH-ENERGY HEAVY-IONS IN HTSC - THEIR EFFECT ON IRREVERSIBILITY LINE AND PINNING PROPERTIES

The defects induced by high energy heavy ions have been studied by high resolution electron microscopy. Columnar amorphous defects of 7 nm in diameter have thus been characterized in the case of 6 GeV-Pb ion irradiation of Y-123, Bi-2212 and Tl-2212 superconductors. Because of their diameter close to the coherence length xi and their shape similar to the vortex core they have been demonstrated as the best pinning centers that can be introduced in HTSC. Drastic changes of the magnetic hysteresis and critical current density are thus reported. Volume pinning force modifications and strong shifts of the irreversibility line have been studied as a function of the temperature and the columnar defect density i.e. the ion dose. The magnetiC field dependence of the critical current density has been discussed on the basis of a competition between pinning and vortex repulsion.