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.

Spin-Orbital-Intertwined Nematic State in FeSe

“…Due to the absence of a magnetic order, a simple orbital-driven nematic order has been proposed to understand the nematic transition in FeSe [33]. In this case, a trivial SOC effect will be expected with a negligible in-plane anisotropy for spin susceptibility, which should be simply scaled with the orbital order [36,60]. Clearly, this is inconsistent with our observation.…”

“…This case was verified by the RPA calculation in BaFe 2 As 2 by only considering a ferro-orbital order without invoking spin d.o.f. [36]. In this situation, the above conjecture is naturally satisfied.…”

“…1(b) and 1(c)]. Because of SOC, the local spin susceptibility is expected to gain a slight anisotropy in each domain [36] (indicated as a pink ellipse in < Sa > vs < S b > plot). The dynamic spin correlation is coupled with the orbital order and shows an anisotropic nature.…”

Effect of Biaxial Strain on the Phase Transitions of Ca(Fe1−xCox)Böhmer1, Sapkota2, Kreyßig3 et al. 2017Phys. Rev. Lett.281340View full textAdd to dashboardCite

“…Recently, new piezo-based strain-tuning devices have been presented [7,8] and used in the study of ruthenates [9,10] and SmB 6 [11]. Additionally, strain has been famously employed to probe the nematic susceptibility of iron-based superconductors [12][13][14][15][16]. Applying strain means enforcing a deformation, or length change with respect to a 'free' reference state, and can be achieved using a rigid device.…”

Nematic Fluctuations in Optimally Doped BaFe1.87Co0.13As2 Observed in Photoinduced Reflectivity Change

“…Previous studies on the ultrafast dynamics suggest that the component of τ ∼ 1 ps is common in Fe‐based materials with spin and/or orbital order at low temperature . The ultrafast dynamics in underdoped Ba(Fe,Co) 2 As 2 showed that a nematic signal of a relaxation time of a few tens of ps shows up below the structural phase‐transition temperature T S , whereas the fast one of τ ∼ 1 ps develops only below the magnetic phase‐transition temperature T N < T S .…”