RECOUPLING OF DECOUPLED VORTEX LIQUID BY COLUMNAR DEFECTS IN BI2SR2CACU2O8+Y

We report on the effect of columnar defects on the interlayer phase co herence in Bi2Sr2CaCu2O8+y using Josephson plasma resonance as a probe . In the vortex liquid phase close to T-c, the resonance field (H-p) s hows a characteristic exponential temperature dependence similar to th at of the irreversibility line. A drastic increase in H-p occurs at a frequency-dependent temperature in the vortex liquid phase. We interpr et this change as a manifestation of field-induced recoupling of decou pled vortex liquid by columnar defects. The double resonance peaks obs erved in this temperature range indicate the coexistence of coupled an d decoupled vortex regions. [S0031-9007(97)04419-0].