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 sharp change in the inductive voltage in the vicinity of the irreversibility line at fields below 60 mT and temperatures above about 40 K is observed. The effects of ac frequency, dc field, and the orientation of the applied dc field with respect to the c axis are investigated. This sharp feature appears to be similar to the melting transition recently 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.