Magnetic Excitation Spectra inBaFe2As2: A Two-Particle Approach within a Combination of the Density Functional Theory and the Dynamical Mean-Field Theory Method

Abstract

We study the magnetic excitation spectra in the paramagnetic state of BaFe$_{2}$As$_{2}$ from the \textit{ab initio} perspective. The one-particle excitation spectrum is determined within the combination of the density functional theory and the dynamical mean-field theory method. The two-particle response function is extracted from the local two-particle vertex function, also computed by the dynamical mean field theory, and the polarization function. This method reproduces all the experimentally observed features in inelastic neutron scattering (INS), and relates them to both the one particle excitations and the collective modes. The magnetic excitation dispersion is well accounted for by our theoretical calculation in the paramagnetic state without any broken symmetry, hence nematic order is not needed to explain the INS experimental data.