Abstract
Differential resistivity, I-V characteristics, and voltage noise have been measured to study the vortex dynamics in Bi2Sr2CaCu2O8+x single crystals. The sample shows a crossover from three to two dimensional behaviour as the magnetic field is higher than a crossover field of 365 Oe. Below the crossover field, the sample show a vortex lattice melting in pinned vortex state as well as in the flux flow state. During the melting, a remarkable voltage noise was observed. The I-V curve measurements reveal that the irreversibility line does not overlap with the melting ling in H-T plane. The separation between these two lines is greatly enhanced when the applied field is over the crossover field.