We present measurements of the angular dependence of the irreversible magnetization of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ single crystals with columnar defects inclined with respect to the c axis. At high fields a sharp maximum centered at the tracks direction is observed. At low fields we identify a lock-in phase characterized by an angle-independent pinning strength and observe an angular shift of the peak towards the c axis that originates in the misalignment between vortices and applied field in anisotropic materials. The interplay among columnar defects, twins, and intrinsic pinning by the ab planes generates a variety of staircase structures. We show that correlated pinning dominates for all orientations of the applied field.

• Received 29 December 1998

DOI:https://doi.org/10.1103/PhysRevB.59.13620