Nematic spin correlations in the tetragonal state of uniaxial strained BaFe2-xNixAs2

TL;DR

This study reveals that in BaFe2-xNixAs2, low-energy spin excitations become anisotropic in the tetragonal phase, correlating with resistivity anisotropy and suggesting a link to superconductivity.

Contribution

It demonstrates a direct connection between spin excitation anisotropy and resistivity anisotropy in iron pnictides using inelastic neutron scattering.

Findings

Spin excitations change from four-fold to two-fold symmetry.

Resistivity and spin anisotropies vanish near optimal superconductivity.

Spin anisotropy is likely linked to the electronic nematic phase.

Abstract

Understanding the microscopic origins of electronic phases in high-transition temperature (high-Tc) superconductors is important for elucidating the mechanism of superconductivity. In the paramagnetic tetragonal phase of BaFe2-xTxAs2 (where T is Co or Ni) iron pnictides, an in-plane resistivity anisotropy has been observed. Here we use inelastic neutron scattering to show that low-energy spin excitations in these materials change from four-fold symmetric to two-fold symmetric at temperatures corresponding to the onset of the in-plane resistivity anisotropy. Because resistivity and spin excitation anisotropies both vanish near optimal superconductivity, we conclude that they are likely intimately connected.