Large pinning efficiency of orthogonal columnar defects in a weakly anisotropic high-T-c superconductor

The pinning efficiency of orthogonal columnar defects has been investigated in weakly anisotropic Tl2/3Bi1/3Sr2CaCu2O7 Single crystals [denoted as (Tl , Bi)-1212 hereafter]. Columnar defects were introduced by heavy ion irradi ation along two directions tilted by 45 degrees from the c axis. This confi guration was compared to a crystal irradiated along the c axis. The whole d amaged volume was the same in both samples. Magnetic measurements, performe d with H//c, show that the perpendicularly crossed defects exhibit the high est pinning efficiency in a wide range of fields and temperatures. To analy ze this enhancement, which can be related to the splay of crossed defects a nd/or to the enlargement of the defect section in the (a,b) planes associat ed with the tilt angle, the (Tl, Bi)-1212 single crystals were compared to a third one, irradiated along one direction only, tilted by 45 degrees from the c axis. Furthermore, these crystals have been compared to a similar se t of defect configurations in YBa2Cu3O7, for a tilt angle of 10 degrees, fo r which a splay effect has already been demonstrated. [S0163-1829(99)13241- 7].