LAUSR

Abstract Utilizing high-resolution electron energy-loss spectroscopy (HREELS) we measure the phonon frequencies of β–FeSe(001), cleaved under ultra-high vacuum conditions. At the zone center ( Γ ¯ –point) three prominent loss features are observed at loss energies of about  ≃ 20.5 and 25.6 and 40 meV. Based on the scattering selection rules we assign the observed loss features to the A1g, B1g, and A2u phonon modes of β–FeSe(001). The experimentally measured phonon frequencies do not agree with the results of density functional based calculations in which a nonmagnetic, a checkerboard or a strip antiferromagnetic order is assumed for β–FeSe(001). Our measurements suggest that, similar to the other Fe-based materials, magnetism has a profound impact on the lattice dynamics of β–FeSe(001).