Nematic-Fluctuation-Mediated Superconductivity Revealed by Anisotropic Strain in Ba(Fe1-xCox )(2)As-2

Anisotropic strain is an external field capable of selectively addressing the role of nematic fluctuations in promoting superconductivity. We demonstrate this using polarization-resolved elasto-Raman scattering by probing the evolution of nematic fluctuations under strain in the normal and superconducting state of the paradigmatic iron-based superconductor a(Fe1 - xCox )(2)As-2 . In the parent compound BaFe2As2 we observe a strain-induced suppression of the nematic susceptibility which follows the expected behavior of an Ising order parameter under a symmetry breaking field. For the superconducting compound, the suppression of the nematic susceptibility correlates with the decrease of the critical temperature T-c, indicating a significant contribution of nematic fluctuations to electron pairing. Our results validate theoretical scenarios of enhanced T-c near a nematic quantum critical point.