Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe1.9Ni0.1As2

TL;DR

This study investigates how spin excitation anisotropy in uniaxially strained BaFe1.9Ni0.1As2 varies with energy and temperature, revealing a large energy scale for spin-driven nematic correlations that influence resistivity anisotropy.

Contribution

It demonstrates that spin excitation anisotropy persists below 60 meV in uniaxial-strained BaFe1.9Ni0.1As2, suggesting spin Ising-nematic correlations drive electronic nematicity.

Findings

Spin excitation anisotropy exists below ~60 meV.

Energy scale of anisotropy exceeds band splitting near optimal doping.

Spin correlations likely drive resistivity anisotropy.

Abstract

We use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe$_{1.9}$Ni$_{0.1}$As$_2$ near optimal superconductivity ($T_c=20$ K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nematic phase, exists for energies below $\sim$60 meV in uniaxial-strained BaFe$_{1.9}$Ni$_{0.1}$As$_2$. Since this energy scale is considerably larger than the energy splitting of the $d_{xz}$ and $d_{yz}$ bands of uniaxial-strained Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ near optimal superconductivity, spin Ising-nematic correlations is likely the driving force for the resistivity anisotropy and associated electronic nematic correlations.