By using effective-medium approaches, we obtain the onset of the electrical-resistivity rounding, above the normal-superconducting transition, associated with inhomogeneities of the mean-field critical temperature ${\mathit{T}}_{\mathit{c}0}$ at scales larger than the superconducting correlation length. These results are compared with available data in single-crystal and single-phase (to within 4%) polycrystalline ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ samples. This comparison shows that the measured resistivity rounding cannot be explained by these types of local ${\mathit{T}}_{\mathit{c}0}$ inhomogeneities. Complementarily, our calculations allow us to check some proposals on ${\mathit{T}}_{\mathit{c}0}$ inhomogeneities associated with local sample strains or oxygen-content variations. The interplay between ${\mathit{T}}_{\mathit{c}0}$ inhomogeneities and superconducting order-parameter fluctuations (SCOPF) leads to the conclusion that in the mean-field-like region (MFR) above the superconducting transition, the ${\mathit{T}}_{\mathit{c}0}$ inhomogeneity contribution to the measured resistivity rounding in high-quality (single-phase) cuprate oxide superconductors is negligible. In contrast, our analysis confirms that in the MFR these effects may be explained quantitatively on the grounds of the Lawrence-Doniach theory for SCOPF.

• Received 11 March 1991

DOI:https://doi.org/10.1103/PhysRevB.43.10560