Accommodation of vortices to tilted line defects in high-Tcsuperconductors with various electronic anisotropies

Columnar defects (CD{close_quote}s) inclined at 45{degree} from the {ital c} axis have been introduced in single crystals of different compounds: Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, Tl{sub 2/3}Bi{sub 1/3}Sr{sub 2}CaCu{sub 2}O{sub 7}, and YBa{sub 2}Cu{sub 3}O{sub 7}. In each case, hysteresis loops have been recorded with the magnetic field parallel to the columns ({ital H}{searrow}{sub {ital a}}{parallel}CD) and perpendicular to them ({ital H}{searrow}{sub {ital a}}{perpendicular}CD). Two regimes are evidenced: an isotropic pinning enhancement [{ital J}{sub {ital c}}({ital H}{searrow}{sub {ital a}}{perpendicular}CD){equivalent_to}{ital J}{sub {ital c}}({ital H}{searrow}{sub {ital a}}{parallel}CD)] at low temperatures and a directional effect [{ital J}{sub {ital c}}({ital H}{searrow}{sub {ital a}}{perpendicular}CD){lt}{ital J}{sub {ital c}}({ital H}{searrow}{sub {ital a}}{parallel}CD)] at higher temperatures. The isotropic regime is ascribed to the occurrence of a {open_quote}{open_quote}totally adjusted{close_quote}{close_quote} state where the vortices zigzag between the CD{close_quote}s and the {ital ab} planes, keeping their mean direction 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 more » CD{close_quote}s in the case {ital H}{sub {ital a}}{perpendicular}CD. {copyright} {ital 1996 The American Physical Society.} « less