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

Abstract

High-temperature superconductivity in the Fe-based materials emerges when the antiferromagnetism of the parent compounds is suppressed by either doping or pressure. Closely connected to the antiferromagnetic state are entangled orbital, lattice, and nematic degrees of freedom, and one of the major goals in this field has been to determine the hierarchy of these interactions. Here we present the direct measurements and the calculations of the in-plane uniform magnetic susceptibility anisotropy of BaFe₂As₂, which help in determining the above hierarchy. The magnetization measurements are made possible by utilizing a simple method for applying a large symmetry-breaking strain, based on differential thermal expansion. In strong contrast to the large resistivity anisotropy above the antiferromagnetic transition at T_N, the anisotropy of the in-plane magnetic susceptibility develops largely below T_N. Our results imply that lattice and orbital degrees of freedom play a subdominant role in these materials.