Origin of in-plane anisotropy in optical conductivity for antiferromagnetic metallic phase of iron pnictides

We examine the optical conductivity in antiferromagnetic (AFM) iron pnictides by mean-field calculation in a fiveband 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.