Influence of twin boundaries and randomly oriented correlated disorder on the liquid vortex plasticity ofYBa2Cu3O7

Abstract

The influence of two strong and interacting pinning contributions on melt-textured ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ (MTG-Y123) has been studied in the liquid vortex state. Twin boundary pinning has been analyzed in terms of oriented correlated disorder, while ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}/{\mathrm{Y}}_{2}{\mathrm{BaCuO}}_{5}$ interfaces behave as randomly oriented correlated disorder. The latter is a consequence of the micronic and spherical ${\mathrm{Y}}_{2}{\mathrm{BaCuO}}_{5}$ (Y211) particles embedded in the ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ (Y123) matrix. Angular magnetoresistance measurements on samples with different content of Y211 particles have allowed us to separate both contributions, to determine the role of each type of defect, and to define the active defect region in the magnetic phase diagram. This analysis has enabled a definition of a source of quenched disorder in Y123, i.e., the randomly oriented correlated disorder. We prove that Y123/Y211 interfaces play the role of this randomly oriented correlated quenched disorder in MTG-Y123 which induces an upward shift of the irreversibility line and vortex activation energy for all the directions of the applied magnetic field. Results of vortex dynamics have been analyzed in terms of plastic mechanisms promoting vortex motion. In addition, we demonstrate a nonvanishing interaction between both types of correlated pinning disorder. Particularly, this is manifested when determining the ratio between the activation energy and the thermal energy at the solid-liquid vortex transition, and estimating the twin boundary pinning energy.