Origin of the resistive anisotropy in the electronic nematic phase of BaFe$_2$As$_2$ revealed by optical spectroscopy

TL;DR

This study uses optical spectroscopy under uniaxial stress to investigate the origin of resistive anisotropy in BaFe$_2$As$_2$, revealing that Fermi surface anisotropy primarily drives the electronic nematic phase's transport properties.

Contribution

It demonstrates that Fermi surface anisotropy, rather than scattering rate changes, is the main cause of resistive anisotropy in the nematic phase of BaFe$_2$As$_2$, using optical spectroscopy.

Findings

Resistive anisotropy in the AFM state is mainly due to spectral weight effects.

In the tetragonal phase, anisotropy is driven by stress-induced Fermi surface changes.

Fermi surface anisotropy is primary in the nematic state.

Abstract

We perform, as a function of uniaxial stress, an optical-reflectivity investigation of the representative 'parent' ferropnictide BaFe$_2$As$_2$ in a broad spectral range, across the tetragonal-to-orthorhombic phase transition and the onset of the long-range antiferromagnetic order (AFM). The infrared response reveals that the $dc$ transport anisotropy in the orthorhombic AFM state is determined by the interplay between the Drude spectral weight and the scattering rate, but that the dominant effect is clearly associated with the metallic spectral weight. In the paramagnetic tetragonal phase, though, the $dc$ resistivity anisotropy of strained samples is almost exclusively due to stress-induced changes in the Drude weight rather than in the scattering rate, definitively establishing the anisotropy of the Fermi surface parameters as the primary effect driving the $dc$ transport properties in the electronic nematic state.