The vortex phase diagram of optimally doped untwinned YBa2Cu3Oy is studied. We find a first-order transition TL(H) in the vortex liquid above the terminal point Hmcp (≃7 T) of both the vortex glass line Tg(H) and the field-driven disordering transition line H*(T). The obtained small entropy change (∼0.02 kB/vortex/layer) and the critical endpoint Hcep (≃11 T) of the TL(H) line indicate that the vortex liquid undergoes the vortex slush regime before the solidification into the vortex glass phase. Below Hmcp, the vortex liquid phase shows the first-order melting transition into the Bragg glass phase. We also study the oxygen content y dependence of the vortex phase diagram and find that the vortex slush regime is located in the borderline (i.e., 6.90≤y≤6.92) below which the vortex lattice melting transition disappears. The result indicates that the point disorder with the intermediate strength plays an important role in the vortex slush regime.
|Number of pages||7|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2002 Dec 1|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics