Quantum criticality in iron pnictides involves both the nematic and antiferromagnetic degrees of freedom, but the relationship between the two types of fluctuations has yet to be clarified. Here we study this problem in the presence of a small external uniaxial potential, which breaks the C4-symmetry in the B1g sector. We establish an identity that connects the spin excitation anisotropy, which is the difference of the dynamical spin susceptibilities at Q1=(π,0) and Q2=(0,π), with the dynamical magnetic susceptibility and static nematic susceptibility. Using this identity, we introduce a scaling procedure to determine the dynamical nematic susceptibility in the quantum critical regime, and illustrate the procedure for the case of the optimally Ni-doped BaFe2As2[Y. Song \textit{et al.}, Phys. Rev. B 92, 180504 (2015)]. The implications of our results for the overall physics of the iron-based superconductors are discussed.
@article{arxiv.1910.14597,
title = {Quantum critical nematic fluctuations and spin excitation anisotropy in iron pnictides},
author = {Chia-Chuan Liu and Elihu Abrahams and Qimiao Si},
journal= {arXiv preprint arXiv:1910.14597},
year = {2020}
}