Influence of twin boundaries on the phase state and vortex dynamics near the melting point in YBa2Cu3O7-delta single crystals

It is found that at temperatures above the melting point of the vortex latt ice T-m and below the temperature T-p corresponding to the onset of pinning on twin boundaries, the current-voltage (I-V) characteristics are linear a t low values of the transport current J but are substantially nonlinear at large J. This behavior of the I-V characteristics is interpreted as the coe xistence in the temperature region T-m < T < T-p of a pinned vortex lattice which is formed near the planes of the twin boundary at T < T-p and an unp inned vortex liquid far the planes of twin boundaries. (C) 2001 American In stitute of Physics.