OBSERVATION OF VORTEX FLUCTUATIONS IN THE CUPRATE SUPERCONDUCTOR BI2SR2CACU2O8

Using a micro-Hall probe, measurements of field of first flux penetrat ion H(p) and the critical current density J(c) have been made near T(c ) of superconducting Bi2Sr2CaCu2O8. In the temperature region just bel ow T(c)=86.0 K; T(s) < T < T(c), it was found that H(p) and J(c) are s trongly suppressed, leaving a reversible diamagnetic susceptibility. N o similar effect is observed in YBa2Cu3O7-y which suggests that the hi ghly two-dimensional character of Bi2Sr2CaCu2O8 is responsible for its particular behavior. The results are compared with recent theoretical predictions.