Current-voltage measurements of thinYBa2Cu3O6.9films compared with a modified Ambegaokar-Halperin theory

Abstract

We have measured and interpreted the current-voltage characteristics of several thin ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.9}$ films. They were prepared by metal-organic deposition and microscopy revealed that they had numerous stacking faults. The measurements were taken at temperatures of 77 and 4.2 K in applied magnetic fields varying from 0 to 6 T. Values of ${\mathit{J}}_{\mathit{c}}$ as large as 2 MA/${\mathrm{cm}}^{2}$ were found at 77 K for films with ${\mathit{T}}_{\mathit{c}}$=92 K, whereas values of ${\mathit{J}}_{\mathit{c}}$ as large as 80 MA/${\mathrm{cm}}^{2}$ were found at 4.2 K for the same films. The data were compared with the predictions of a modified Ambegaokar-Halperin model, a conventional power-law model, and a vortex-glass model. The data were generally fit best by the Ambegaokar-Halperin model from which were obtained the resistance of the film, the critical current density, and the pinning potential as functions of the magnetic field and temperature. These parameters varied widely but systematically among the films and were interpreted in terms of differences in their imperfections. The critical current density and pinning potential obtained from this analysis were compared to the same quantities inferred from a more traditional method. The dependencies on the magnetic field were very similar, although the magnitudes were different. The advantage of defining the critical current density in terms of a physical model is emphasized.