Effect of twin boundary density on the vortex melting transition in YBa2Cu3O(7-delta) single crystals

摘要

The authors present magnetotransport (rho)(H,T) measurements in clean untwinned and twinned crystals of YBa(sub 2)Cu(sub 3)O(sub 7(minus)(delta)) in magnetic fields up to 8 Tesla for H (parallel) c. In untwinned crystals, they show strong support for a vortex solid to liquid first order melting transition at a temperature T(sub m), much below the mean field transition temperature T(sub c)(H), characterized by an extremely sharp drop in resistivity (rho)(T(sub m)) and the appearance of hysteretic behavior at (rho)(H(sub m)). In densely twinned crystals, the sharp transition is replaced with a continuous transition at a higher temperature T(sub BG) > T(sub m). Furthermore, the cusp in T(sub BG)((theta)) predicted by the Bose glass theory at fixed field is observed. In dilutely twinned crystals they demonstrate the competing effect of pinning and freezing at the phase transition. The vortex solid state at low fields is characterized by the appearance of a ''peak effect'' just below the melting temperature.