Observation of glass behavior at low fields in polycrystalline YBa2Cu3O7.

Abstract

We have measured the magnetic susceptibility of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ at low fields and observed a glass transition at ${\mathit{T}}_{\mathit{g}}$${\mathit{T}}_{\mathit{c}}$. This glass behavior, which is different from the vortex glass-fluid transition at high fields, can be interpreted as due to a Josephson weak-link effect. ${\mathit{T}}_{\mathit{g}}$ shifts to lower temperatures with increasing applied field and is completely suppressed at higher fields, where \ensuremath{\chi}(T) shows typical diamagnetic behavior. As H\ensuremath{\rightarrow}0, ${\mathit{T}}_{\mathit{g}}$ initially increases as the pressure on the sample pellet is increased and then saturates at higher pellet pressures. The pellet pressure dependence of ${\mathit{H}}_{\mathit{d}}$, the field necessary to suppress the glass state, is qualitatively consistent with theoretical prediction, that is, it is inversely proportional to the projected area normal to the field for an average loop of connected superconducting regions.