Fluctuation‐induced conductivity of melt‐textured Y_0.95Er_0.05Ba₂Cu₃O_7−δ superconductor prepared in air

Abstract

Systematic conductivity measurements near TC in melt‐textured Y0.95Er0.05Ba2Cu3O7−δ superconductors, prepared using the top‐seeding growth technique, are presented. Measurements were performed both for current applied parallel and perpendicular to the c‐axis. Samples with different disorder states were studied and the influences of the erbium addition on conductivity fluctuations are discussed. The microstructural characteristics of samples were analyzed by scanning electron microscopy and X‐ray diffraction, while the superconducting properties were determined by resistivity and dc magnetization measurements. To identify power‐law divergences of the conductivity, the results were analyzed in terms of the temperature derivative of the resistivity (${\rm d}{\rho} /{\rm d}T$) and of the logarithmic temperature derivative of the conductivity (${-} {\rm d(ln}{\Delta} {\sigma} {\rm )}/{\rm d}T$). The fluctuations above the critical temperature are highly anisotropic: Gaussian regimes were observed for the $J//a(b)c$ configuration and critical regimes for the $J//ab$ configuration. Also, for the more disordered state, the data evidenced a two‐stage transition.