Effect of tensile stress on the in-plane resistivity anisotropy in   BaFe2As2
  The effect of uniaxial tensile stress and the resultant strain on the structural/magnetic transition in the parent compound of the iron arsenide superconductor, BaFe$_2$As$_2$, is characterized by temperature-dependent electrical resistivity, x-ray diffraction and quantitative polarized light imaging. We show that strain induces a measurable uniaxial structural distortion above the first-order magnetic transition and significantly smears the structural transition. This response is different from that found in another parent compound, SrFe$_2$As$_2$, where the coupled structural and magnetic transitions are strongly first order. This difference in the structural responses explains the in-plain resistivity anisotropy above the transition in BaFe$_2$As$_2$. This conclusion is supported by the Ginzburg-Landau - type phenomenological model for the effect of the uniaxial strain on the resistivity anisotropy. 
E. C. Blomberg, A. Kreyssig, M. A. Tanatar, R. Fernandes, M. G. Kim,   A. Thaler, J. Schmalian, S. L. Bud'ko, P. C. Canfield...
cond-mat.supr-con