Orbital-Ordering Induces Structural Phase Transition and the Resistivity Anomaly in Iron Pnictides

TL;DR

This paper proposes that orbital ordering causes the structural phase transition and resistivity anomaly in iron pnictides, linking electronic orbital anisotropy to structural and magnetic phenomena observed experimentally.

Contribution

It introduces a model where orbital ordering explains the structural transition, resistivity anomaly, and magnetic properties in iron pnictides, aligning with experimental data.

Findings

Orbital ordering induces the orthorhombic structural phase transition.

Resistivity anomalies are caused by electron scattering from localized orbitals.

The model explains stripe-like antiferromagnetism and magnetic anisotropy.

Abstract

We attribute the structural phase transition (SPT) in the parent compounds of the iron pnictides to orbital ordering. Due to the anisotropy of the $d_{xz}$ and $d_{yz}$ orbitals in the $xy$ plane, a ferro-orbital ordering makes the orthorhombic structure more energetically favorable, thus inducing the SPT. In this orbital-ordered system, the sites with orbitals that do not order have higher energies. Scattering of the itinerant electrons by these localized two-level systems causes a resistivity anomaly upon the onset of the SPT. The proposed orbital ordering also leads to the stripe-like anti-ferromagnetism and anisotropy of the magnetic exchanges. This model is quantitatively consistent with available experimental observations.