# Highly anisotropic quasiparticle interference patterns in the spin-density wave state of the iron pnictides

## TL;DR

This study models impurity-induced quasiparticle interference in the spin-density wave state of iron pnictides, revealing highly anisotropic patterns consistent with experimental observations, using a five orbital tight-binding and mean field approach.

## Contribution

It introduces a detailed theoretical analysis of impurity effects on quasiparticle interference in iron pnictides, highlighting anisotropic patterns and their origin.

## Key findings

- Impurities cause spatial LDOS modulations with ~8a_Fe-Fe periodicity.
- Quasiparticle interference patterns are anisotropic with peaks at (~±π/4,0).
- Pattern origin traced to elliptical constant energy contours in electronic structure.

## Abstract

We investigate the impurity scattering induced quasiparticle interference in the ($\pi, 0$) spin-density wave phase of the iron pnictides. We use a five orbital tight binding model and our mean field theory in the clean limit captures key features of the Fermi surface observed in angle-resolved photoemission. We use a t-matrix formalism to incorporate the effect of doping induced impurities on this state. The impurities lead to a spatial modulation of the local density of states about the impurity site, with a periodicity of $\sim 8a_{{\rm Fe}-{\rm Fe}}$ along the antiferromagnetic direction. The associated momentum space quasiparticle interference pattern is anisotropic, with major peaks located at $\sim (\pm \pi/4,0)$, consistent with spectroscopic imaging scanning tunneling microscopy. We trace the origin of this pattern to an elliptical contour of constant energy around momentum (0,0), with major axis oriented along the (0,1) direction, in the mean field electronic structure.