ANGLE-RESOLVED TRANSPORT MEASUREMENTS IN A BI-2212 CRYSTAL WITH INCLINED COLUMNAR DEFECTS - STUDY OF THE DIRECTIONAL EFFECTS

Columnar defects at 45 degrees with respect to the ab planes have been installed in a Bi-2212 single crystal by 5.8 GeV Pb ion irradiation. Transport measurements have been carried out in the so-called ''top'' and ''cross'' configurations, as a function of the temperature T, the magnetic field B, the current i and theta, the angle between B and the ab planes, In a restricted area of the B-T plane, the R(theta) curves exhibit a marked dip centered along the direction of the columnar def ects, for B lower or close to the fluence equivalent field B-phi t whi ch corresponds to a vortex density equal to the planar density of the columnar defects, The directional features become less pronounced as t he field or the temperature increase, and disappear completely above a crossover line which extrapolates at low fields to a temperature lowe r than T-c. This crossover is discussed in terms of a decorrelation of line vortices induced by thermal fluctuations.