Dimer Impurity Scattering, "Reconstructed" Nesting and Density-Wave Diagnostics in Iron Pnictides

TL;DR

This paper presents a theory explaining impurity-induced nanoscale electronic structures in iron pnictides, linking STM observations to a reconstructed Fermi surface and hidden density-wave order, providing new insights into their microscopic origins.

Contribution

It introduces a theoretical framework connecting impurity resonances with reconstructed Fermi pockets and hidden density-wave order in iron pnictides, supported by experimental STM data.

Findings

Dimer resonances align with reconstructed Fermi pockets

Impurity patterns break C4 symmetry consistent with PoDW order

Nanoscale structures serve as diagnostics for hidden orders

Abstract

While the impurity-induced nanoscale electronic disorder has been extensively reported in the underdoped iron pnictides, its microscopic origins remain elusive. Recent scanning tunneling microscopy (STM) measurements reveal a dimer-type resonant structure induced by cobalt doping. These dimers are randomly distributed but uniformly aligned with the antiferromagnetic a axis. A theory of the impurity-induced quasiparticle interference patterns is presented that shows the local density of states developing an oscillatory pattern characterized by both geometry and orbital content of the {\em reconstructed} Fermi pockets, occasioned by the pocket density-wave (PoDW) order along the b axis. This pattern breaks the $C_4$ symmetry and its size and orientation compare well with the dimer resonances found in the STM experiments, hinting at the presence of a "hidden" PoDW order. More broadly, our theory spotlights such nanoscale structures as a useful diagnostic tool for various forms of order in iron pnictides.