superconductor*

Hole doping by substituting Ba for K in BaFe₂As₂ parent compound results in a very complex phase diagram that includes nematic, stripe, orthorhombic (C2) and tetragonal (C4) antiferromagnetic phases with substantial doping intervals where these phases coexist with superconductivity. We use controlled uniaxial strain (mechanical) and artificial disorder (induced by electron irradiation) to study the interplay of these phases in the under-doped compositions. Experimentally, anisotropic in-plane resistivity was measured in high quality single crystals of (Ba_1-xK_x)Fe₂As₂ in pristine state and after low-temperature electron irradiation. Polarized optical microscopy was used to visualize the evolution of structural domains and correlate it with transport studies.