Short-Range Nematic Correlations in Iron-Based Superconductors Probed by Pair Distribution Function Analysis

Elucidating the role of nematicity in iron-based superconductors (FeSCs) remains a crucial objective in the field. Nematic fluctuations are thought to be present across wide regions of the FeSC phase diagrams, with possible connections to the superconducting mechanism. However, detecting and characterizing nematic fluctuations poses a significant experimental challenge. Here, we show that atomic pair distribution function (PDF) analysis of neutron and x-ray total scattering data can be a powerful tool to investigate nematic fluctuations. We report on temperature-dependent PDF measurements of representative iron pnictide and chalcogenide systems, which reveal ubiquitous nanometer-scale orthorhombic distortions of the instantaneous local structure even in phases with an average tetragonal structure. These distortions of the local structure reflect the large nematic susceptibility in FeSCs and may have significant implications for superconductivity and neighboring phases in these materials.