Quantum critical nematic fluctuations and spin excitation anisotropy in iron pnictides

TL;DR

This paper investigates the relationship between nematic and magnetic fluctuations at quantum criticality in iron pnictides, establishing a new identity linking spin excitation anisotropy with nematic susceptibility, and applying it to doped BaFe2As2.

Contribution

The study introduces a novel identity connecting spin anisotropy with nematic susceptibility and develops a scaling method to measure dynamical nematic susceptibility in quantum critical regimes.

Findings

Established an identity linking spin excitation anisotropy with nematic susceptibility.

Developed a scaling procedure to determine dynamical nematic susceptibility.

Applied the method to Ni-doped BaFe2As2, providing insights into iron-based superconductors.

Abstract

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 $C_4$-symmetry in the B$_{1g}$ sector. We establish an identity that connects the spin excitation anisotropy, which is the difference of the dynamical spin susceptibilities at $\vec{Q}_1=\left(\pi,0\right)$ and $\vec{Q}_2=\left(0,\pi\right)$, 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 BaFe$_2$As$_2$[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.