Nematic Correlation Length in Iron-Based Superconductors Probed by Inelastic X-Ray Scattering

Nematicity is ubiquitous in electronic phases of high-T-c superconductors, particularly in the Fe-based systems. We used inelastic x-ray scattering to extract the temperature-dependent nematic correlation length. from the anomalous softening of acoustic phonon modes in FeSe, underdoped Ba(Fe0.97Co0.03)(2)As-2, and optimally doped Ba(Fe0.94Co0.06)(2)As-2. In all cases, we find that. is well described by a power law (T - T-0)(-1/2) extending over a wide temperature range. Combined with the previously reported Curie-Weiss behavior of the nematic susceptibility, these results point to the mean-field character of the nematic transition, which we attribute to a sizable nematoelastic coupling that is likely detrimental to superconductivity.