Phonon spectrum of SrFe2As2 determined using multizone phonon refinement

TL;DR

This study measures the phonon spectrum of SrFe2As2 using advanced neutron scattering techniques, finding that magnetic order does not significantly affect phonon energies above 23 meV, and confirming the accuracy of DFT predictions.

Contribution

The paper introduces a multizone phonon refinement method to accurately measure phonon energies and assesses the impact of magnetic order on phonons in SrFe2As2.

Findings

Phonon energies determined with ~0.1 meV accuracy.

DFT calculations qualitatively match experimental phonon energies.

No observable effect of magnetic transition on high-energy phonons.

Abstract

The ferropnictide superconductors exhibit a sensitive interplay between the lattice and magnetic degrees of freedom, including a number of phonon modes that are much softer than predicted by nonmagnetic calculations using density functional theory (DFT). However, it is not known what effect, if any, the long-range magnetic order has on phonon frequencies above 23 meV, where several phonon branches are very closely spaced in energy and it is challenging to isolate them from each other. We measured these phonons using inelastic time-of-flight neutron scattering in ~40 Brillouin zones, and developed a technique to determine their frequencies. We find this method capable of determining phonon energies to ~0.1 meV accuracy, and that the DFT calculations using the experimental structure yield qualitatively correct energies and eigenvectors. We do not find any effect of the magnetic transition on these phonons.