Correlation Between Local Structure and Interlayer Coupling Through Fluctuations-Induced Conductivity in La0.7Sr0.3MnO3-Added (Bi, Pb)-2223 Superconductors

In this study, we investigated the relationship between excess conductivity and the local structure of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ ((Bi, Pb)-2223) polycrystalline samples. A series of (Bi, Pb)-2223 + LSMO composites (0 – 1.5 wt%) were synthesized using the conventional solid-state reaction method. The critical temperature (T_c) determined from the temperature-dependent resistivity curves decreased with increasing LSMO content, from 106.65 K for the pure sample to 102.48 K to the 15 wt% sample, except for the 10 wt% sample, which exhibited a rise comparable to the pure sample. To elucidate the mechanisms affecting T_c, we applied the Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) theories. We identified the Lawrence-Doniach temperature (T_LD) as the crossover point at which the system transitions from 2 to 3D fluctuations in the mean field region (MFR). Our calculations of excess conductivity within the MFR enabled us to quantify microscopic parameters such as the coherence length along the c-axis (\({\xi }_{c}\)), interlayer coupling strength (\(J\)), and interlayer coupling distance (\(d\)), revealing trends in T_c associated with LSMO addition in the (Bi, Pb)-2223 system. The local atomic structure of the CuO₂ plane was characterized using X-ray absorption fine structure measurements at the Cu K-edge. We observed contrasting behaviors between the Cu–O and Cu-Ca bonds, indicating weakened interaction between the CuO₂ superconducting layer and the space layer. Meanwhile, the Cu-Sr bond exhibited suppression or elongation due to LSMO addition. Notably, in the 10 wt% sample, the bond lengths from the absorbing atom were similar to those in the pure sample, suggesting an inhomogeneous distribution of LSMO in the samples. These findings indicate that local structural alterations due to LSMO addition decrease the carrier supply to the CuO₂ layers, thereby affecting the superconducting properties of the (Bi, Pb)-2223 system.