Elasto-Raman scattering: Arsenic optical phonon as a probe of nematicity in BaFe2As2

We report a Raman scattering study of nematic degrees of freedom in the iron-based superconductor parent compound BaFe2As2 under tunable uniaxial strain. We demonstrate that the polarization resolved arsenic (As) phonon intensity can be used to monitor the nematic order parameter as a function of both temperature and strain. At low temperature in the nematic ordered phase, we use it to track the continuous and reversible orientation of nematic domains under variable strain. At higher temperatures, the evolution of the As phonon intensity under strain reflects an enhanced nematic susceptibility close to the nematic transition TS. Its temperature dependence under strong strain qualitatively follows the expected behavior of an Ising order parameter under a symmetrybreaking field. Our elasto-Raman study illustrates the interest of combining selective anisotropic strain with a symmetry-resolved probe like Raman scattering. Elasto-Raman scattering can be applied to a wide variety of quantum materials where uniaxial strain tunes electronic orders.