Conductivity anisotropy in the antiferromagnetic state of iron pnictides

TL;DR

This paper investigates the origin of in-plane resistivity anisotropy in iron pnictides, finding that Fermi surface topology and Fermi velocity anisotropy, rather than orbital ordering, likely explain the experimental observations.

Contribution

The study calculates the Drude weight ratio in a five-band model, showing its dependence on Fermi surface features and challenging the orbital ordering hypothesis.

Findings

Drude weight ratio D_x/D_y varies between 0.3 and 1.4.

Orbital ordering favors an anisotropy opposite to experiments.

Fermi velocity anisotropy likely explains the observed conductivity anisotropy.

Abstract

Recent experiments on iron pnictides have uncovered a large in-plane resistivity anisotropy with a surprising result: the system conducts better in the antiferromagnetic x direction than in the ferromagnetic y direction. We address this problem by calculating the ratio of the Drude weight along the x and y directions, Dx/Dy, for the mean-field Q=(\pi,0) magnetic phase diagram of a five-band model for the undoped pnictides. We find that Dx/Dy ranges between 0.3 < D_x/D_y < 1.4 for different interaction parameters. Large values of orbital ordering favor an anisotropy opposite to the one found experimentally. On the other hand D_x/D_y is strongly dependent on the topology and morfology of the reconstructed Fermi surface. Our results points against orbital ordering as the origin of the observed conductivity anisotropy, which may be ascribed to the anisotropy of the Fermi velocity.