Origin of In-Plane Anisotropy in Optical Conductivity for Antiferromagnetic Metallic Phase of Iron Pnictides

TL;DR

This study uses mean-field calculations on a five-band Hubbard model to explain the in-plane anisotropy in optical conductivity observed in antiferromagnetic iron pnictides, highlighting the role of orbital characters and Dirac dispersions.

Contribution

It provides a theoretical explanation for the origin of in-plane anisotropy in optical conductivity in AFM iron pnictides, linking orbital and Dirac dispersion effects.

Findings

Optical conductivity is higher along the AFM direction at low energies.

At higher energies, the conductivity along the FM direction surpasses the AFM direction.

Orbital characters and Dirac dispersions are key to understanding the anisotropy.

Abstract

We examine the optical conductivity in antiferromagnetic (AFM) iron pnictides by mean-field calculation in a five-band Hubbard model. The calculated spectra are well consistent with the in-plane anisotropy observed in the measurements, where the optical conductivity along the direction with the AFM alignment of neighboring spins is larger than that along the ferromagnetic (FM) direction in the low-energy region; however, that along the FM direction becomes larger in the higher-energy region. The difference between the two directions is explained by taking account of orbital characters in both occupied and unoccupied states as well as of the nature of Dirac-type linear dispersions near the Fermi level.