Influence of Al2O3–15 wt%ZrO2 nanocomposite addition on pseudogap characteristics in Bi1·6Pb0·4Sr2Ca2Cu3O10+δ superconductor

This study, employing the local pair model, examines how the Al₂O₃–15 wt%ZrO₂ nanocomposite affects the pseudogap peculiarities and temperature dependence of fluctuation-induced conductivity in the Bi_1·6Pb_0·4Sr₂Ca₂Cu₃O_10+δ superconductor. The fluctuation-induced conductivity survey reveals that the experimental data for both undoped samples and those doped with low concentrations (0.0–1.0 wt%) of the Al₂O₃–15 wt%ZrO₂ nanocomposite are well explained by the 3D Aslamazov-Larkin (AL) and 2D Maki-Thompson (MT) models, with 2D fluctuations being the most significant in all samples. The results indicate that samples with 0.1 and 0.2 wt% additives exhibit a wider region of 2D fluctuations than the undoped sample. This suggests that a minor addition of nanocomposite promotes the formation of phase-coherent fluctuating Cooper pairs. The value and temperature variation of the pseudogap Δ∗(T) for different composites were deduced using the local pairs model based on experimental fluctuation-induced conductivity data. It was observed that the transition temperature from the Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) regimes of local pairs, T_pair, rose from 117.5 K at the undoped sample to approximately 133.5 K at the composite containing 0.2 wt% additive. However, with higher additive concentrations, T_pair decreased, reaching 120.5 K at the composite containing 1.0 wt% additive. The estimated superconducting gap value at T = 0, Δ(0), rose from 250 K (21.5 meV) for the undoped sample to 254 K (21.9 meV) at the composite including 0.2 wt% additive, then dropped to 243 K (20.9 meV) at the composite including 1.0 wt% additive.