Local avalanche-like superconducting transitions in YBCO

AC susceptibility has been measured simultaneously in three different regio ns of YBCO ceramic samples in the presence of strong thermal gradient. A lo cal step-like perturbation, applied in addition to the monotonic temperatur e decrease, results in local avalanche-like transitions. The superconductin g regions enlarge much faster than the propagation of the thermal waves. We suggest that the adiabatic magnetic flux avalanches reflect creation of ne w superconducting, amplitude-correlated domains by stimulated correlation o f the order parameter phase. (C) 2000 Elsevier Science B.V. All rights rese rved.