Accommodation of vortices to tilted line defects in high-T-c superconductors with various electronic anisotropies

Columnar defects (CD's) inclined at 45 degrees from the c axis have been introduced in single crystals of different compounds: Bi2Sr2CaCu2O8, Tl2Ba2CaCu2O8, Tl2Ba2Ca2Cu3O10, Tl2/3Bi1/3Sr2CaCu2O7, and YBa2Cu3O7. In each case, hysteresis loops have been recorded with the magnetic field parallel to the columns <((H)over right arrow (a) parallel to CD)> and perpendicular to them <((H)over right arrow (a) perpendicular to CD)>, Two regimes are evidenced an isotropic pinning enhancement <[J(c)((H)over right arrow (a) perpendicular to CD)> = <J(c)((H)over right arrow> (a) parallel to CD)]> at low temperatures and a directional effect <[J(c)((H)over right arrow> (a) perpendicular to CD)> < <J(c)((H)over right arrow (a) parallel to CD)]> at higher temperatures. The isotropic regime is ascribed to the occurrence of a ''totally adjusted'' state where the vortices zigzag between the CD's and the ab planes, keeping their mean direct ion along the applied field. An analysis is proposed for the crossover between these two regimes, which accounts for the observed influences of the temperature and electronic anisotropy. The vanishing of the difference between the two configurations at zero field is discussed in terms of a complete reorientation of the vortices along the CD's in the case H-a perpendicular to CD.