Magnetic and Quasiparticle Excitation Spectra of an Itinerant $J_1-J_2$ Model for Iron Pnictide Superconductors

TL;DR

This paper models the magnetic and quasiparticle excitation spectra of an itinerant J1-J2 model for iron pnictides, revealing a second optical spin-wave branch, anisotropic spin-wave velocity, and Dirac cones in the quasiparticle spectrum, relevant to experimental observations.

Contribution

It introduces a detailed calculation of magnetic and quasiparticle spectra for the J1-J2 model, highlighting novel features like the optical branch and Dirac cones.

Findings

Presence of an optical spin-wave branch

Planar directional anisotropy in spin-wave velocity

Dirac cones in quasiparticle spectrum

Abstract

We calculate the magnetic and quasiparticle excitation spectra of an itinerant $J_1-J_2$ model for iron pnictides. In addition to an acoustic spin-wave branch, the magnetic spectrum has a second, optical branch, resulting from the coupled four-sublattice magnetic structure. The spin-wave velocity has also a planar directional anisotropy, due to the collinear/striped antiferromagnetism. Within the magnetically ordered phase, the quasiparticle spectrum is composed of two Dirac cones, resulting from the folding of the magnetic Brillouin zone. We discuss the relevance of our findings to the understanding of both neutron scattering and photoemission spectroscopy results for SrFe$_{2}$As$_{2}$.