Soft Phonons Reveal The Nematic Correlation Length In Ba(Fe0.94c0.06)(2)As-2

Nematicity is ubiquitous in electronic phases of high-T-c superconductors, particularly in the Fe-based systems. While several experiments have probed nematic fluctuations, they have been restricted to uniform or momentum-averaged fluctuations. Here, we investigate the behavior of finite-momentum nematic fluctuations by utilizing the anomalous softening of acoustic phonon modes in optimally doped Ba(Fe0.94Co0.06)(2)As-2. We determine the nematic correlation length and find that it sharply changes its T dependence at T-c, revealing a strong connection between nematicity and superconductivity.