INTEGRATED ULTRASONIC ELASTICITY AND SUPERCONDUCTING FLUCTUATION ANALYSIS OF EUBA2CU3O7−Δ SYSTEMS: A METHODOLOGICAL FRAMEWORK FOR CU-O CHAIN DYNAMICS

Abstract

We present an integrated theoretical and experimental framework linking high-temperature lattice dynamics with low-temperature superconducting fluctuation paraconductivity in rare-earth barium copper oxide systems, with a focus on EuBa₂Cu₃O_7−δ (Eu-123). By combining acoustic wave velocity measurements with the Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models, we analyze the structural and electronic contributions of the basal plane Cu-O chains. At high temperatures, a prominent step-like elastic anomaly is observed at 260 K during cooling of pristine Eu-123, which is attributed to first-order oxygen ordering into superstructures within the Cu-O chains. Reducing the oxygen content to δ = 0.7 or substituting trivalent Al³⁺ directly into the Cu (1) chain site destroys this oxygen ordering, suppressing the step-like anomaly and restoring pure Lakkad-type anharmonic behavior. In contrast, adding submicron-sized Al₂O₃ nanoparticles as an intergranular phase preserves the step-like anomaly but shifts it to 200 K, while introducing a localized lattice instability at 240 K. To demonstrate the low-temperature electrical paraconductivity, we present a paraconductivity analysis based on the transition parameters of the studied Eu-123 phases. The paraconductivity fits reveal that disrupting oxygen ordering intrinsically via Al³⁺ substitution collapses the interlayer Josephson coupling parameter J from 0.055 to 0.012 and compresses the c-axis coherence length from 1.38 Å to 0.64 Å, trapping the Cooper-pair fluctuations in a quasi-two-dimensional (2D) regime. Conversely, intergranular Al₂O₃ addition maintains a three dimensional (3D) coupling profile (J∼0.040). This integrated characterization framework provides solid-state physicists with a non-destructive method to map the relationship between lattice strain and superconducting phase coherence.