Phonon anomalies in FeS

TL;DR

This study investigates lattice dynamics in tetragonal FeS using light scattering, revealing phonon modes, their temperature dependence, and evidence of magnetic order and electron-phonon interactions.

Contribution

The paper combines experimental light scattering data with lattice-dynamical simulations and symmetry analysis to elucidate phonon behavior and electron-phonon coupling in FeS.

Findings

Identification of Raman active phonon modes in FeS

Observation of phonon energy increase below 20K indicating magnetic order

Evidence of significant electron-phonon interaction affecting two-phonon excitations

Abstract

We present results from light scattering experiments on tetragonal FeS with the focus placed on lattice dynamics. We identify the Raman active A1g and B1g phonon modes, a second order scattering process involving two acoustic phonons, and contributions from potentially defect-induced scattering. The temperature dependence between 300 and 20K of all observed phonon energies is governed by the lattice contraction. Below 20K the phonon energies increase by 0.5-1 cm$^{-1}$ thus indicating putative short range magnetic order. Along with the experiments we performed lattice-dynamical simulations and a symmetry analysis for the phonons and potential overtones and find good agreement with the experiments. In particular, we argue that the two-phonon excitation observed in a gap between the optical branches becomes observable due to significant electron-phonon interaction.