We theoretically examine anisotropy of in-plane resistivity in the striped antiferromagnetic phase of an iron arsenide superconductor by applying a memory function approach to the ordered phase with isotropic nonmagnetic impurity. We find that the an
isotropy of the scattering rate is independent of carrier density when the topology of the Fermi surface is changed after the introduction of holes. On the other hand, the anisotropy of the Drude weight monotonically decreases reflecting the distortion of the Dirac Fermi surface and eventually leads to the reverse of anisotropy of resistivity, being consistent with experiment. The origin of the anisotropy is thus attributed to the interplay of impurity scattering and anisotropic electronic states.
We theoretically investigate spin dynamics and $L_3$-edge resonant inelastic X-ray scattering (RIXS) of Chromium with commensurate spin-density wave (SDW) order, based on a multi-band Hubbard model composed of 3$d$ and 4$s$ orbitals. Obtaining the gr
ound state with the SDW mean-field approximation, we calculate the dynamical transverse and longitudinal spin susceptibility by using random-phase approximation. We find that a collective spin-wave excitation seen in inelastic neutron scattering hardly damps up to $sim$0.6 eV. Above the energy, the excitation overlaps individual particle-hole excitations as expected, leading to broad spectral weight. On the other hand, the collective spin-wave excitation in RIXS spectra has a tendency to be masked by large spectral weight coming from particle-hole excitations with various orbital channels. This is in contrast with inelastic neutron scattering, where only selected diagonal orbital channels contribute to the spectral weight. However, it may be possible to detect the spin-wave excitation in RIXS experiments in the future if resolution is high enough.
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 opti
cal 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.
