Vortex pinning and columnar defects in superconducting oxides

Heavy ions irradiation of oxides can create columnar defects, i.e. amorphous tracks of about 100 A in diameter. These columnar defects are very efficient pinning centers for vortices in superconducting oxides: the critical current density is enhanced by a large amount and the irreversibility line which limits the possibility of any application is shifted to higher magnetic fields. In this paper, we review the creation of columnar defects by ion irradiation in YBaCuO, Bi-based and Tl-based superconducting oxides. We present the modification of the superconducting properties induced by the presence of such defects. Since the defects are very well controlled in shape and density, they provide a unique model system to investigate the pinning properties in high Tc superconductors. (orig.)