6533b7d6fe1ef96bd12665a1

RESEARCH PRODUCT

Relation between microstructure and transport properties of epitaxial YBa2Cu3O7-d thin films.

subject

description

Abstract In order to understand the origin of the high critical current densities observed in thin superconducting films compared to single crystals we measured in several epitaxial YBa 2 Cu 3 O 7−δ thin films the magnetic field and temperature dependence of the superconducting current density j s and the dynamical relaxation rate Q ≡ d ln j s / d ln( d B/ dt ). For all samples we found that (i) the superconducting current density j s is independent of magnetic field up to a certain field B Φ . The value of this field, which is sample dependent, decreases with increasing temperature; (ii) for fields B>B Φ , the superconducting current density falls off as B −1/2 over several decades; (iii) Q exhibits a sharp decrease for B B Φ and (iv) Q is essentially constant for B > B Φ . These results can be understood in terms of strong pinning. Based on structural information obtained by AFM and STM we propose a model to explain both the high value and the magnetic field dependence of j s and Q .