Q-dependence of the spin fluctuations in the intermediate valence compound CePd3.

We report inelastic neutron scattering experiments on a single crystal of the intermediate valence compound CePd3. At 300 K the magnetic scattering is quasielastic, with half-width Γ = 23 meV, and is independent of momentum transfer Q. At low temperature, the Q-averaged magnetic spectrum is inelastic, exhibiting a broad peak centered near Emax = 55 meV. These results, together with the temperature dependence of the susceptibility, 4f occupation number, and specific heat, can be fit by the Kondo/Anderson impurity model. The low temperature scattering near Emax, however, shows significant variations with Q, reflecting the coherence of the 4f lattice. The intensity is maximal at (1/2, 1/2, 0), intermediate at (1/2, 0, 0) and (0, 0, 0), and weak at (1/2, 1/2, 1/2). We discuss this Q-dependence in terms of current ideas about coherence in heavy fermion systems.

Irreversible dynamics of the phase boundary in U(Ru0.96Rh0.04)2Si2 and implications for ordering.

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru0.96Rh0.04)2Si2, which yield irreversible properties similar to those at the valence transition of Yb(1-x)Y(x)InCu4. To explain these similarities, we propose a bootstrap mechanism by which lattice parameter changes caused by an electric quadrupolar order parameter within phase II become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition.

Localized excitation in the hybridization gap in YbAl3.

The intermediate valence compound YbAl3 exhibits a broad magnetic excitation in the inelastic neutron scattering spectrum with characteristic energy E1 approximately 50 meV, equal to the Kondo energy (T(K) approximately 600-700 K). In the low temperature (T < T(coh) approximately 40 K) Fermi liquid state, however, a new peak in the scattering occurs at E2 approximately 33 meV, which lies in the hybridization gap that exists in this compound. We report inelastic neutron scattering results for a single-crystal sample. The scattering at energies near E1 qualitatively has the momentum (Q) dependence expected for interband scattering across the indirect gap. The scattering near E2 has a very different Q dependence: it is a weak function of Q over a large fraction of the Brillouin zone and is smallest near (1/2,1/2, 1/2). A possibility is that the peak at E2 arises from a spatially localized excitation in the hybridization gap.