Spin excitation anisotropy as a probe of orbital ordering in the paramagnetic tetragonal phase of superconducting BaFe1.904Ni0.096As2

TL;DR

This study uses polarized neutron scattering to reveal that in-plane spin excitations in electron-doped BaFe1.904Ni0.096As2 become anisotropic above magnetic and structural transition temperatures, indicating a link to orbital ordering.

Contribution

It demonstrates that spin excitation anisotropy can serve as a probe for electronic anisotropy and orbital ordering in the tetragonal phase of iron-based superconductors.

Findings

Spin excitations become anisotropic above magnetic and structural transition temperatures.

Superconductivity enhances anisotropy in spin excitations along specific directions.

Spin excitation anisotropy is independent of antiferromagnetic order and lattice distortion.

Abstract

We use polarized neutron scattering to demonstrate that in-plane spin excitations in electron doped superconducting BaFe1.904Ni0.096As2 (Tc=19.8 K) change from isotropic to anisotropic in the tetragonal phase well above the antiferromagnetic (AF) ordering and tetragonal-to-orthorhombic lattice distortion temperatures (Tn=Ts=33 K) without an uniaxial pressure. While the anisotropic spin excitations are not sensitive to the AF order and tetragonal-to-orthorhombic lattice distortion, superconductivity induces further anisotropy for spin excitations along the [1,1,0] and [1,-1,0] directions. These results indicate that the spin excitation anisotropy is a probe of the electronic anisotropy or orbital ordering in the tetragonal phase of iron pnictides.