Dynamic Magnetic Response of Heavy Fermion Semimetals

We have calculated the dynamical magnetic response of a model of a heavy fermion semimetal, which is characterized by a narrow gap in the f density of states and a low conduction electron density of states at the Fermi energy. The model is used to fit optical absorbtion measurements on $CeRu_{4}Sb_{12}$ performed by Dordevic {\it et al.}, Phys. Rev. Lett. {\bf 86}, 684 (2001). The temperature dependence of the dissipative part of the magnetic response is compared with the experimentally determined inelastic neutron scattering cross-section of $CeRu_{4}Sb_{12}$ measured by Adroja {\it et al.} Phys. Rev. B {\bf 68}, 099426 (2003).