Superconducting Fluctuations and Excess Conductivity Analysis of Te-Substituted TlSr2(Ca1−x Te x )Cu2O7−δ

Abstract

Samples with nominal starting compositions TlSr2(Ca1−xTex)Cu2O7−δ (x = 0.05–0.30) were prepared by the solid-state reaction method and studied by powder X-ray diffraction and electrical resistance measurements. The purpose of this work was to determine the valence state of Te in the TlSr2CaCu2O7−δ (Tl-1212) phase. It is also to determine the dimension of fluctuation-induced conductivity λ, and the superconducting fluctuations and excess conductivity using the Aslamazov–Larkin (AL) theory. The Lawrence–Donaich (LD) theory was used to calculate the coherence length ξc(0), interlayer coupling J, and anisotropy γ = (ξab(0)/ ξc(0)). X-ray powder diffraction patterns indicated that the samples were dominantly Tl-1212 phase. Temperature-dependent resistance measurements showed metallic normal-state behavior for all samples. The onset transition temperature, Tc onset, was between 32 K (x = 0.05) and 61 K (x = 0.25). The valence of Te in Tl-1212 is suggested to be Te6+ from the analysis of the highest Tc in the x = 0.25 sample. Excess conductivity analyses showed that Te substitution induced 2D-to-3D conductivity transition with the highest transition temperature, T2D−3D observed for x = 0.25. The calculations based on Lawrence–Doniach model showed the shortest coherence length, ξc(0), and highest anisotropy (γ = 10.24) for the x = 0.25 sample.