Lattice dynamics in FeSe via inelastic x-ray scattering and first-principles calculations

TL;DR

This study combines inelastic x-ray scattering and first-principles calculations to investigate phonons in FeSe, revealing that including spin-polarization in DFT improves agreement with experiments despite the lack of magnetic order.

Contribution

It demonstrates that spin-polarized DFT better models FeSe phonons, highlighting the importance of spin fluctuations in its lattice dynamics.

Findings

Discrepancy between experimental phonons and non-magnetic DFT.

Spin-polarized DFT improves phonon dispersion agreement.

Spin fluctuations are significant in FeSe's lattice behavior.

Abstract

We report an inelastic x-ray scattering investigation of phonons in FeSe superconductor. Comparing the experimental phonon dispersion with density functional theory (DFT) calculations in the non-magnetic state, we found a significant disagreement between them. Improved overall agreement was obtained by allowing for spin-polarization in the DFT calculations, despite the absence of magnetic order in the experiment. This calculation gives a realistic approximation, at DFT level, of the disordered paramagnetic state of FeSe, in which strong spin fluctuations are present.