Enhancement of interlayer phase coherence in the vortex liquid state of Bi(2)Sr(2)CaCu(2)O(8+y)with columnar defects

We studied the phase coherence in the vortex liquid state of Bi2Sr2 CaCu2 O 8+y with columnar defects (CDs) using Josephson plasma resonance. The phase coherence as a function of magnetic field is nonmonotonic in samples with higher density of CDs, and we observe multiple resonance peals in a limited temperature range. The characteristic field H* for the enhancement of the phase coherence normalized by the matching field (B-Phi) is constant betwee n 1/5 and 1/3 for samples with larger B-Phi, while H* is constant in sample s with smaller Be. In samples with CDs introduced at angles from the c-azis , H* is determined only by the density of CDs in the CuO2 layers. In a samp le with CDs at 80 degrees from the c-axis, a large enhancement of the phase coherence was observed when the field is applied parallel to the direction of CDs and clear triple resonance pears are observed.