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

TL;DR

This study reveals that in hole-doped iron pnictides, the in-plane resistivity anisotropy reverses sign with increased doping, aligning with theories on anisotropic electron scattering by spin fluctuations.

Contribution

It demonstrates the doping-dependent sign reversal of resistivity anisotropy in hole-doped iron pnictides, a phenomenon not observed in electron-doped counterparts.

Findings

Resistivity anisotropy diminishes with doping

Sign reversal of resistivity anisotropy occurs at high doping levels

Results agree with theoretical models of anisotropic spin-fluctuation scattering

Abstract

The in-plane anisotropy of the electrical resistivity across the coupled orthorhombic and magnetic transitions of the iron pnictides has been extensively studied in the parent and electron-doped compounds. All these studies universally show that the resistivity $\rho_{a}$ across the long orthorhombic axis $a_{O}$ - along which the spins couple antiferromagnetically below the magnetic transition temperature - is smaller than the resistivity $\rho_{b}$ of the short orthorhombic axis $b_{O}$, i. e. $\rho_{a}<\rho_{b}$. Here we report that in the hole-doped compounds Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, as the doping level increases, the resistivity anisotropy initially becomes vanishingly small, and eventually changes sign for sufficiently large doping, i. e. $\rho_{b}<\rho_{a}$. This observation is in agreement with a recent theoretical prediction that considers the anisotropic scattering of electrons by spin-fluctuations in the orthorhombic/nematic state.