Flux jump avalanches in torque studies of single crystal YBa2Cu3O7-delta

A series of avalanche-like jumps are observed in the mixed state of single crystal YBa2Cu3O7-delta (YBCO) superconductors. Emerging as a saw-tooth pat tern in torque vs. sample orientation in magnetic field, these jumps are di scontinuous on our most resolute angular scale. While reminiscent of the cl assical flux jump instability, the present jumps are instead proposed to be associated with the layered nature of the material and twin boundary (TB) pinning, the combination of which promotes a crossover from a tilted to a k inked vortex structure. (C) 1999 Elsevier Science B.V. All rights reserved.