Interlayer phase coherence in the vortex matter phases of Bi₂Sr₂CaCu₂O_8+y

The vortex matter phase diagram in Bi2Sr2CaCu2O8+y is studied by the magnetization, measurements and by Josephson plasma resonance. Above the first-order transition (FOT), sample-moving magnetization measurements show an anomaly suggesting the surface-barrier related transition (Tx line). We find a strong change in the interlayer phase coherence at the FOT and the second peak lines, indicating the decoupling nature of these lines. However, we find no anomaly in the interlayer phase coherence at the Tx line. These results rule out the existence of the vortex line liquid state. © 2000 Elsevier Science B-V All rights reserved.