Low-energy phonon dispersion in LaFe4Sb12

We studied the vibrational dynamics of a single crystal of LaFe4Sb12 by three-axis inelastic neutron spectroscopy. The dispersion of phonons with wave vectors q along [xx0] and [xxx] directions in the energy range of eigenmodes with high amplitudes of lanthanum vibrations, i.e., at h omega less than or similar to 12 meV is identified. Symmetry-avoided anticrossing dispersion of phonons is established in both monitored directions and distinct eigenstates at high-symmetry points and at the Brillouin-zone center are discriminated. The experimentally derived phonon dispersion and intensities are compared with and backed up by ab initio lattice dynamics calculations. Results of the computer model match well with the experimental data.