In- and out-of-plane vortex correlations in YBa2Cu3O7.

Abstract

Transport measurements in the mixed state of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ crystals (H\ensuremath{\parallel}c) using the ``dc-flux-transformer'' configuration show that the glass-liquid phase transition at the irreversibility line, ${\mathit{T}}_{\mathit{i}}$(H), behaves as a three-dimensional vortex phase transition. These results together with resistance measurements in the c direction show that the vortex correlation across the sample is destroyed at a temperature ${\mathit{T}}_{\mathrm{th}}$(H), higher than ${\mathit{T}}_{\mathit{i}}$(H). However, the dependence of ${\mathit{T}}_{\mathrm{th}}$(H) on sample thickness suggests that, in real thermodynamic phase transitions (infinite sample), the long-range correlation in the ab plane, as well as in the c direction, is lost at the single temperature ${\mathit{T}}_{\mathit{i}}$(H).