Inelastic neutron scattering and lattice dynamical calculations in BaFe2As2

TL;DR

This study uses inelastic neutron scattering and lattice dynamical calculations to analyze phonon behavior in BaFe2As2 across temperature changes and under pressure, revealing a harmonic phonon system and predicting phonon shifts due to doping and pressure.

Contribution

First extensive measurement of phonon density of states in BaFe2As2 with theoretical modeling, linking phonon behavior to structural and magnetic transitions.

Findings

No significant change in phonon spectra between 10 K and 200 K.

Shell model calculations agree with experimental phonon spectra.

Phonon energies shift under pressure and doping as predicted.

Abstract

We report here first extensive measurements of the temperature dependence of phonon density of states of BaFe2As2, the parent compound of the newly discovered FeAs-based superconductors, using inelastic neutron scattering. The experiments were carried out on the thermal time-of-flight neutron spectrometer IN4 at the ILL on a polycrystalline sample. There is no appreciable change in the spectra between T = 10 K and 200 K, although the sample undergoes a magnetic as well as a tetragonal-to-orthorhombic structural phase transition at 140 K. This indicates a rather harmonic phonon system. Shell model lattice dynamical calculations based on interatomic potentials are carried out to characterize the phonon data. The calculations predict a shift of the Ba-phonons to higher energies at 4 GPa. The average energy of the phonons of the Ba-sublattice is also predicted to increase on partial substitution of Ba by K to Ba0.6K0.4. The calculations show good agreement with the experimental phonon spectra, and also with the specific heat data from the literature.