Electronic Scattering Effects in Europium-Based Iron Pnictides

TL;DR

This study uses infrared spectroscopy to analyze electronic scattering in EuFe₂(As₁₋ₓPₓ)₂, revealing how magnetic order and phosphor substitution influence carrier dynamics and electronic structure.

Contribution

It provides new insights into the effects of magnetic ordering and isovalent substitution on electronic scattering and band structure in EuFe₂As₂-based pnictides.

Findings

Suppression of the low-energy SDW gap feature.

High-energy Hund's coupling feature is sensitive to SDW order.

Phosphor substitution induces a Lifshitz transition affecting scattering rates.

Abstract

In a comprehensive study, we investigate the electronic scattering effects in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ by using Fourier-transform infrared spectroscopy. In spite of the fact that Eu$^{2+}$ local moments order around $T_\text{Eu} \approx 20$\,K, the overall optical response is strikingly similar to the one of the well-known Ba-122 pnictides. The main difference lies within the suppression of the lower spin-density-wave gap feature. By analysing our spectra with a multi-component model, we find that the high-energy feature around 0.7\,eV -- often associated with Hund's rule coupling -- is highly sensitive to the spin-density-wave ordering, this further confirms its direct relationship to the dynamics of itinerant carriers. The same model is also used to investigate the in-plane anisotropy of magnetically detwinned EuFe$_{2}$As$_{2}$ in the antiferromagnetically ordered state, yielding a higher Drude weight and lower scattering rate along the crystallographic $a$-axis. Finally, we analyse the development of the room temperature spectra with isovalent phosphor substitution and highlight changes in the scattering rate of hole-like carriers induced by a Lifshitz transition.