INTERLAYER JOSEPHSON COUPLING OF THERMALLY EXCITED VORTICES IN BI2SR2CACU2O8-Y

Measurements of the zero-field resistive transition of Bi2Sr2CaCu2O8 s ingle crystals suggest that a bulk zero-resistance state develops thro ugh a sequential process characterized by two transition temperatures. The upper transition corresponds to Josephson coupling of parallel Cu O bilayers, and the lower transition to the conventional Kosterlitz-Th ouless dissociation of bound vortex excitations. Measurements using a ''flux transformer'' electrode geometry indicate a pronounced peak in the secondary voltage, which is suppressed by an external magnetic fie ld.