•C. Meingast1, R. Lortz1,2, A.I. Rykov3,
T. Matsui3 und S. Tajima3
1Forschungszentrum Karlsruhe, Institut für Festkörperphysik,
2Fakultät für Physik, Universität Karlsruhe,
76131
3ISTEC, 10-13 Shinonome I-Chome, Koto-ku, Tokyo 135, Japan
The H-T phase diagram of the high-temperature superconductor YBa2Cu3Ox is investigated using high-resolution dilatometry in fields up to 11 Tesla. In clean single crystals the first-order melting transition is clearly seen in both the thermal expansion and the magnetostriction data. This coupling of the vortex lattice to the crystal lattice demonstrates that the vortex melting transition is a transition of the whole superconductor and not just a transition of the vortex lattice sitting in an inactive crystal host. The melting transition is replaced by a kinetic glass transition for samples with sufficient pinning centers. We show that this glass transition is in some sense similar to conventional glass transitions observed in supercooled liquids and then discuss implications of our results for the phase diagram of YBa2Cu3Ox.