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.
@article{arxiv.1712.02724,
title = {Phonon anomalies in FeS},
author = {A. Baum and A. Milosavljević and N. Lazarević and M. M. Radonjić and B. Nikolić and M. Mitschek and Z. Inanloo Maranloo and M. Šćepanović and M. Grujuić-Brojčin and N. Stojilović and M. Opel and Aifeng Wang and C. Petrovic and Z. V. Popović and R. Hackl},
journal= {arXiv preprint arXiv:1712.02724},
year = {2018}
}