Magnetic Excitations of a Nodally-Hybridized Heavy-Fermion Semi-Metal: Application to CeNiSn and UNiSn.

We examine the magnetic excitations of an Anderson Lattice Model with a V-shaped pseudogap due to nodal hybridization. The model produces a V-shaped pseudogap in the electron density of states close to the Fermi-Energy, similar to the low-temperature density of states inferred from NMR, break-junction and specific heat measurements on CeNiSn. CeNiSn has been described as a nodally hybridized semi-metal with a finite density of states in the pseudogap. The existence of low-dimensional Fermi-Surface has been inferred from measurements of Shubnikov-de Haas oscillations. The low-dimensional Fermi-surface has been attributed to the existence of metallic surface states, however, photoemission experiments indicate that the Fermi-surface is due to bulk-states. Inelastic neutron scattering experiments also show the existence of a spin-gap and unusual magnetic excitations. The interpretations of the experimental results are controversial. The ALM model with nodal hybridization exhibits degenerate pairs of one-dimensional Fermi-surface located at the center of the pseudogap in accordance with the findings of photoemission experiments. At energies slightly off the Fermi-energy, the constant energy cuts open up and develop into tori with small areas. We calculate the static and dynamic magnetic susceptibilities which show that the system exhibits distinct types of magnetic excitations that compare favorably with the experimentally observed spectra for CeNiSn and the AFM ordered compound UNiSn.