Effect of Strains of Differing Symmetry on the Coupled Nematic/Structural Phase Transition for Underdoped compositions of Co-doped BaFe₂As₂

We investigate the effect of strains of differing symmetry on the critical temperature (T_s) of the coupled nematic/structural phase transition of Ba(Fe_1-xCo_x)₂As2. By comparing the response of T_s under two different sets of strain conditions, corresponding to hydrostatic pressure (up to 2.5GPa) and uniaxial stress (applied along the [100] tetragonal axis up to 0.5% strain), we are able to fully decompose the response with respect to the two symmetric strains (ε_A1g,1 = (ε_xx+ε_yy)/2 and ε_A1g,2 = ε_zz), and one antisymmetric strain (ε_B1g = (ε_xx-ε_yy)/2). We find a linear dependence of Ts for hydrostatic conditions, implying that for symmetric strains up to at least 0.9%, the material remains in the linear regime. However, a non-linear dependence is observed for samples held under uniaxial stress, providing evidence that antisymmetric strain ε_B1g also affects Ts, consistent with a Landau Free Energy analysis.