Anisotropy of the DC conductivity due to orbital-selective spin fluctuations in the nematic phase of iron superconductors

TL;DR

This paper investigates how orbital-selective spin fluctuations influence the anisotropy of dc conductivity in the nematic phase of iron superconductors, revealing competing effects from scattering rates and Fermi velocity modifications.

Contribution

It introduces a comprehensive model linking spin fluctuations, orbital ordering, and conductivity anisotropy, accounting for opposite contributions from scattering and Fermi velocity changes.

Findings

Conductivity anisotropy arises from both scattering rate and Fermi velocity modifications.

These two effects contribute with opposite signs to the anisotropy.

The model explains differences in anisotropy observed in 122 and FeSe compounds.

Abstract

We study the dc conductivity of iron-based superconductors within the orbital-selective spin fluctuation scenario. Within this approach, the anisotropy of spin fluctuations below the spin-nematic transition at T$_S$ is also responsible for the orbital ordering, induced by nematic self-energy corrections to the quasiparticle dispersion. As a consequence, the anisotropy of the dc conductivity below T$_S$ is determined not only by the anisotropy of the scattering rates as expected within a spin-nematic scenario, but also by the modification of the Fermi velocity due to the orbital reconstruction. More interestingly, it turns out that these two effects contribute to the dc-conductivity anisotropy with opposite signs. By using realistic band-structure parameters we compute the conductivity anisotropy for both 122 and FeSe compounds, discussing the possible origin of the different dc-conductivity anisotropy observed experimentally in these two families of iron-based superconductors.