FIELD-DRIVEN COUPLING TRANSITION IN THE VORTEX STATE OF IRRADIATED BI2SR2CACUO8 - COMPUTER-SIMULATION STUDY

We examine a vortex phase diagram for high-T-c superconductor Bi2Sr2Ca Cu2O8 when columnar defects are introduced by heavy-ion irradiation, b y using Monte Carlo simulation based on the Lawrence-Doniach model. At finite temperatures, we numerically find a magnetic-held-driven disco ntinuous transition in the trapping rate of ''pancake'' vortices to th e defects, at a critical field of B/B-Phi similar or equal to 1/3 belo w the matching field B-Phi. The transition in the Vortex liquid phase is accompanied by a discontinuous jump of the interlayer coherence, wh ere the decoupled vortex liquid appears to partially couple along the defects.