Critical currents and flux creep in yttrium barium(2) copper(3) oxide(7-delta) superconducting thin films.

摘要

Transport critical currents are not a fundamental property of superconductors. Rather, critical currents in superconducting materials are determined by a variety of considerations, including fundamental thermodynamic properties and the microstructure of the material. The motivation for the present work is both technological, since high transport critical currents are essential for many applications, and fundamental. We investigate the effect of changing various parameters in the film growth recipe, with the goal of being able to make known changes in the structure of in-situ grown films. The basic features of synthesis, critical currents, and flux creep in typical films are measured and characterized. Systematic changes in the microstructure of the films are made, which are then related, in some instances, to observed critical currents and flux creep. A serious difficulty with establishing relationships of this sort is that vortex interactions with the high T{dollar}sb{lcub}rm c{rcub}{dollar} materials and the mechanisms for pinning are not well understood. As a partial remedy, the analysis of flux pinning potentials is developed to a level of sophistication which is suitable for application to high temperature superconductors. The applicability of this analysis to high T{dollar}sb{lcub}rm c{rcub}{dollar} superconducting thin films is investigated, and the model is then applied to the study of oxygen deficient YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}7-delta{rcub}{dollar} thin films.