In-plane anisotropy and possible chain contribution to magnetoconductivity in YBa₂Cu₃O_7-δ

The magnetoresistivity of untwinned YBa₂Cu₃O_7-δ single crystals was measured in magnetic fields up to 12 T, for B∥c and B∥ab, at temperatures up to T_c+84K and T_c+50K, respectively. Two issues were addressed; determination of the in-plane coherence length anisotropy γ=ξ_b/ξ_a and discussion of the role of the CuO chains in the magnetoconductivity Δσ. A fluctuation conductivity theory that allows for an in-plane coherence length anisotropy (ξ_a≠ξ_b), as well as an extension of the usual Aronov-Hikami-Larkin theory that does not, were used in analyses. The results suggest that the anisotropy γ is close to 1. The analyses also suggest a contribution to the magnetoconductivity from the CuO chains of a sign which depends on the direction between field and current.