Determination of In-Plane Anisotropy from Magnetoresistivity Measurements on YBa2Cu3O7−δ

The magnetoresistance of six untwinned YBa2Cu3O7−δcrystals has been measured above TcforI⊥B‖c. Fluctuation theories allowing for an in-plane coherence length anisotropy (ξa≠ ξb) were used in the analyses. The results suggest that the anisotropy, γ = ξb/ξa, is considerably lower than that expected from the resistivity ratio, i.e.,\(\gamma < \sqrt {\rho _a /\rho _b } \). Some magnetoresistive measurements with the field in the ab-plane are also presented.