Study of the hybridization gap in a heavy fermion compound: CeRu ₄Sb₁₂

We have investigated the temperature and momentum dependence of the inelastic neutron scattering response of CeRu₄Sb₁₂. Our neutron scattering study shows the opening of a Q-independent spin gap of 30meV in the excitation spectrum, which is smaller than the charge gap of 47 meV observed in optical studies. The spin gap is nearly temperature independent below 100 K, while above this temperature the gap starts to fill up and at higher temperatures the magnetic response becomes purely quasielastic. We discuss the origin of the spin gap and consider the difference between the magnitude of the spin and charge gaps on the basis of theoretical models.