Coupling transition of the vortex liquid in Bi2Sr2CaCu2O8+delta with columnar defects

The interlayer Josephson coupling in the vortex fluid phase of heavy-ion irradiated Bi2Sr2CaCu2O8+delta is probed by Josephson plasma resonance. The introduction of columnar defects changes the nature of the vortex liquid dramatically. We show that two types of vortex liquid, the well-coupled and the decoupled pancake vortex liquids, appear in the irradiated crystals. The pancake vortices tend to couple with increasing magnetic field, which is opposite to the pristine crystal. The double resonance peaks appear as a function of field in a narrow temperature range well above the irreversibility line. This implies an occurrence of the coupling transition in the liquid phase. [S0031-9007(97)04422-0].