FIRST-ORDER DECOUPLING TRANSITION IN THE VORTEX LATTICE OF BI2SR2CACU2O8 FROM LOCAL MUTUAL INDUCTANCE MEASUREMENTS

We have used a miniature mutual inductance technique to measure the ac transmittivity Bi2Sr2CaCu2O8 crystals in small applied dc fields. A s harp change in the inductive voltage in the vicinity of the irreversib ility line at fields below 60 mT and temperatures above about 40 K is observed. The effects of ac frequency, dc field, and the orientation o f the applied dc field with respect to the c axis are investigated. Th is sharp feature appears to be similar to the melting transition recen tly observed in local magnetic measurements. We find it is associated with changes in the c-axis resistivity and is consistent with a first- order decoupling transition.