Dichotomy between in-plane magnetic susceptibility and resistivity anisotropies in extremely strained BaFe₂As₂

The in-plane resistivity and uniform magnetic susceptibility anisotropies of $BaFe_{2}As_{2}$ are obtained with a new method, in which a large symmetry-breaking uniaxial strain is applied using a substrate with a very anisotropic thermal expansion. The resistivity anisotropy and its corresponding elastoresistivity exhibit very similar diverging behavior as those obtained from piezo-stack experiments. This suggests that the resistivity anisotropy is more a direct measure of magnetism than of nematicity, since the nematic transition is no longer well-defined under a large strain. In strong contrast to the large resistivity anisotropy above $T_{N}$, the anisotropy of the in-plane magnetic susceptibility develops largely below $T_{N}$. Using an itinerant model, we show that the observed anisotropy ($\chi_{b}>\chi_{a}$) is determined by spin-orbit coupling and the orientation of the magnetic moments in the antiferromagnetic phase, and that the anisotropy is dominated by intra-orbital ($yz,yz$) contributions of the Umklapp susceptibility.