Regular Article

The competition of Hund’s coupling and impurity on transport anisotropy in iron-based superconductors

¹ Humanities Science Center, Southern University of Science and Technology, Shenzhen 518055, P.R. China
² Department of Physics, Beijing Normal University, Beijing 100875, P.R. China

^a e-mail: bjanyang@163.com

Received: 23 July 2018
Received in final form: 21 September 2018
Published online: 9 January 2019

Abstract

The origin of anisotropic transport in the nematic phase of the iron-based superconductors is still controversial. Two main explanations include the extrinsic sources induced by impurity scattering and the intrinsic mechanism which highlights the orbital order or spin scenarios. Based on an inhomogeneous three-orbital Hubbard model, we study the effects of Hund’s coupling and substitutions on the nematic susceptibility and anisotropic conductance. We find that nematic susceptibility is tuned by Hund’s coupling in undoped case and reaches a peak at J∕U = 0.12. However, this anisotropic electron state is fragile and can easily be destroyed by weak doping. The anisotropy of resistivity ρ_anis = (ρ_a∕ρ_b) − 1 rapidly reduces in the small doping level and then gradually increases with doping concentration. However, the twofold nanostructure induced by impurities will be suppressed when we increase the Hund’s coupling, consistent with the scanning tunnelling experiments on iron pnictides. These results also explain the contradictory dependence of ρ_anis on substitutions in tetragonal and orthorhombic phase.