date:RIKEN, Inst Phys & Chem, Photodynam Res Ctr, Aoba Ku, Sendai, Miyagi, Japan; Katholieke Univ Leuven, Lab VSM, B-3001 Louvain, Belgium; ETH Honggerberg, Festkorperphys Lab, CH-8093 Zurich, Switzerland
The vortex correlation along the c-axis of Y124 single crystals has been investigated by using the quasi DC flux transformer configuration. A simultaneous sharp drop associated with the vortex lattice melting is observed in both the primary and secondary voltages. Our results suggest that the vortices just above the melting temperature are three-dimensional line liquid with its correlation length along the c direction l(c) less than or equal to t, the sample thickness. At a temperature T-d, the vortices lose their correlation along the c direction and disserve into 2D pancake vortices. An H-T phase diagram for the Y124 single crystal is obtained.