Effect of impurity on anisotropy of high-Tc superconductivity in YBa2(Cu1-xZnx)3O7-δ single crystals

The effect of Zn doping on anisotropy of high-TC superconductivity is studied in single-crystal YBa2(Cu1-xZnx)3O7-δ (YBCZO) within the range 0<x<0.03. The resistive transition curves under a magnetic field for these impurity-containing systems are successfully described for the first time by the renormalized fluctuation theory including ψ4 term. The derived coherence length ratio ξab/ξc, which indicates anisotropy in superconductivity, decreases as the impurity concentration increases. However, both ρc and the normal state anisotropy ρc/ρab increase. This situation is not consistent with the Lawrence-Doniach (LD) model. The anisotropic 3-D metal model seems to be appropriate for the YBCZO system. This result excludes certain types of high-TC theories which assume strict two dimensionality of the electronic system. (orig.)