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 hig h resolution electron microscopy. Columnar amorphous defects of 7 nm i n diameter have thus been characterized in the case of 6 GeV-Pb ion ir radiation of Y-123, Bi-2212 and Tl-2212 superconductors. Because of th eir diameter close to the coherence length xi and their shape similar to the vortex core they have been demonstrated as the best pinning cen ters that can be introduced in HTSC. Drastic changes of the magnetic h ysteresis and critical current density are thus reported. Volume pinni ng force modifications and strong shifts of the irreversibility line h ave been studied as a function of the temperature and the columnar def ect density i.e. the ion dose. The magnetiC field dependence of the cr itical current density has been discussed on the basis of a competitio n between pinning and vortex repulsion.