Absence of Long-Wavelength Nematic Fluctuations in LiFeAs

We investigated long-wavelength nematic fluctuations in an Fe-based superconductor LiFeAs near q = (0.05, 0, 0) by measuring temperature-dependent renormalization of acoustic phonons through inelastic neutron scattering. We found that the phonons have a conventional behavior, as would be expected in the absence of electronic nematic fluctuations. This observation implies that either electron-phonon coupling is too weak to see any effect or that nematic fluctuations are not present.