Evidence for polarons in iron pnictides of the Ln-1111 and AE-122 families

TL;DR

This paper provides evidence that polarons significantly influence the electrical properties of iron pnictides in the Ln-1111 and AE-122 families, linking their resistivity behavior to spin density wave and lattice transition phenomena.

Contribution

It introduces a polaron-based explanation for the electrical resistivity and phase transitions in iron pnictides, supported by pressure-dependent measurements and theoretical modeling.

Findings

Resistivity data consistent with polaron conduction

Activation energies linearly related to SDW critical temperatures

Landau theory predicts transition order based on T* and T0

Abstract

Examination of the electrical resistivities of iron pnictides shows that they can be accounted by conduction by polarons. Their activation energies show a linear behaviour with the critical temperatures of the spin density waves (SDW), T*, as both vary with pressure. The slope matches the ratio SDW gap to T*, while the intercept can be related to the transition temperature of the lattice distortion, T0. An adapted Landau free energy predicts the observed order of the transitions, according to which is higher, T* or T0. Simple arguments favour combined Jahn-Teller antiferromagnetic bipolarons.