Low-frequency Einstein mode in the heavy-fermion compound UBe13

We present results of inelastic neutron scattering on polycrystalline samples of the heavy-fermion compound U${\mathrm{Be}}_{13}$. We analyze these data on the basis of a Born-von-Kármán model. Our results give clear evidence for the existence of an Einstein-mode-like oscillator at 13 meV, independently of temperature. From our deduced phonon density of states, we calculate the lattice contribution to the low-temperature heat capacity. It is found to be small compared to the electronic part.