Sign-reversal of the in-plane resistivity anisotropy in iron pnictides

TL;DR

This study investigates the in-plane resistivity anisotropy in BaFe$_{2}$As$_{2}$, revealing a sign reversal across the phase diagram, which highlights the complex interplay between magnetism, nematicity, and superconductivity in iron pnictides.

Contribution

It demonstrates the sign change of resistivity anisotropy in BaFe$_{2}$As$_{2}$ across the doping phase diagram, a behavior not observed in other materials, and explains it through Fermi surface reconstruction and spin fluctuations.

Findings

Resistivity anisotropy changes sign across the phase diagram.

Magnetic scattering dominates normal state transport.

Sign reversal linked to Fermi surface and spin fluctuations.

Abstract

The concept of an electronically-driven breaking of the rotational symmetry of a crystal, without involving magnetic order, has found experimental support in several systems, from semiconductor heterostructures and ruthenates, to cuprate and iron-pnictide superconductors. In the pnictide BaFe$_{2}$As$_{2}$, such an "electronic nematic state" appears above the magnetic transition dome, over a temperature range that can be controlled by external strain. Here, by measuring the in-plane resistivity anisotropy, we probe the electronic anisotropy of this material over the entire nematic/magnetic dome, whose end points coincide with the optimal superconducting transition temperatures. Counter-intuitively, we find that, unlike other materials, the resistivity anisotropy in BaFe$_{2}$As$_{2}$ changes sign across the doping phase diagram, even though the signs of the magnetic, nematic, and orthorhombic order parameters are kept fixed. This behavior is explained by the Fermi surface reconstruction in the magnetic phase and spin-fluctuation scattering in the nematic phase. The unique behavior of the transport anisotropy unveils that the primary role is played by magnetic scattering in the normal state transport properties of the iron pnictides, suggesting a close connection between magnetism, nematicity, and unconventional superconductivity.