Intrinsic Local Structure Anisotropy of Bi₂Sr₂CaCu₂O _8+δ Superconductor Probed by Polarized X-Ray Absorption...

We have investigated the local structure of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{O}_{8+\delta }$ superconductor by Cu K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy to explore the temperature-dependent local displacements and their possible relationship with the charge ordering, nematicity, and superconductivity. We have used x-ray polarization dependence of the EXAFS signal to unravel a clear local structure anisotropy, indicating a deviation from the average tetragonal symmetry. This distortion is associated with charge ordering and stripe formation in the ${\mathrm{CuO}}_4$ plane. Anomalies in the Debye-Waller factor at both the charge-ordering and superconducting transition temperatures suggest a strong coupling between the local displacements and electronic degrees of freedom. The local structure anisotropy appears stronger in the interlayer, highlighted by the Cu─Sr bond correlations. These findings provide further insight into the interplay between atomic displacements, charge ordering, and superconductivity in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{O}_{8+\delta }$ , emphasizing the importance of local structural effects in shaping the electronic phase diagram of high- $T_c$ cuprates.