Electronic nematic correlations in the stress free tetragonal state of BaFe$_{2-x}$Ni$_{x}$As$_{2}$

TL;DR

This study reveals that resistivity anisotropy in stress-free tetragonal BaFe$_{2-x}$Ni$_x$As$_2$ arises from magnetoelastic coupling linked to antiferromagnetic order, highlighting the role of lattice distortion and spin correlations.

Contribution

It demonstrates that electronic nematic correlations and resistivity anisotropy exist in stress-free tetragonal iron pnictides, emphasizing the influence of magnetoelastic coupling and magnetic order.

Findings

Resistivity anisotropy persists in stress-free tetragonal phase below T**.

Neutron scattering links anisotropy to antiferromagnetic order.

Local lattice distortions and spin correlations drive resistivity anisotropy.

Abstract

We use transport and neutron scattering to study electronic, structural, and magnetic properties of the electron-doped BaFe$_{2-x}$Ni$_x$As$_2$ iron pnictides in the external stress free detwinned state. Using a specially designed in-situ mechanical detwinning device, we demonstrate that the in-plane resistivity anisotropy observed in the uniaxial strained tetragonal state of BaFe$_{2-x}$Ni$_x$As$_2$ below a temperature $T^\ast$, previously identified as a signature of the electronic nematic phase, is also present in the stress free tetragonal phase below $T^{\ast\ast}$ ($<T^\ast$). By carrying out neutron scattering measurements on BaFe$_2$As$_2$ and BaFe$_{1.97}$Ni$_{0.03}$As$_2$, we argue that the resistivity anisotropy in the stress free tetragonal state of iron pnictides arises from the magnetoelastic coupling associated with antiferromagnetic order. These results thus indicate that the local lattice distortion and nematic spin correlations are responsible for the resistivity anisotropy in the tetragonal state of iron pnictides.