J. M. Lawrence

Valence fluctuation phenomena

Valence fluctuation phenomena occur in rare-earth compounds in which the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration (valence) and/or of the magnetic moment. The authors review the experimental results observed in the subset of such systems for which the 4f ions form a lattice with identical valence on each site. The discussion includes key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering. This is followed by a review of existing theoretical work concerning both the ground states and the isomorphic phase transitions which occur in such compounds; the emphasis is on those aspects which make valence fluctuation phenomena such a challenging many-body problem.

Crystalline electric field effects in Ce M In 5 ( M = Co , Rh , Ir ) : Superconductivity and the influence of Kondo spin fluctuations

We have measured the crystalline electric field (CEF) excitations of the

Evidence for a 'coherence' gap in Ce3Bi4Pt3

\mathrm{Ce}M{\mathrm{In}}_{5}\phantom{\rule{0.3em}{0ex}}(M=\mathrm{Co},\mathrm{Rh},\mathrm{Ir})

Neutron scattering study of crystal fields in CeRhIn5

series of heavy fermion superconductors by means of inelastic neutron scattering. In each case, the CEF excitations are considerably broadened, due to Kondo hybridization of the localized

Hall effect in YbXCu4 and the role of carrier density in the YbInCu4 valence transition

f

Dependence of the effective masses in YbAl3 on magnetic field and disorder

-moments with the conduction electrons. Fits to a phenomenological CEF model reproduce the inelastic neutron scattering spectra and the high-temperature magnetic susceptibility. We also present calculations within the noncrossing approximation (NCA) to the Anderson impurity model, including the effect of CEF level-splitting for the inelastic neutron scattering spectra and the magnetic susceptibility. Our results indicate that the CEF level-splitting in all three materials is similar, and can be thought of as being derived from the cubic parent compound

Magnetic properties of Ce5Si3

\mathrm{Ce}{\mathrm{In}}_{3}

YbIn1-xAgxCu4: Crossover from first-order valence transition to heavy Fermion behavior

in which an excited state quartet at

Low temperature crystal structure of Ce3Al

\ensuremath{\sim}12\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

Speculations on the critical behavior of reduced moment antiferromagnetic cerium compounds (invited)

is split into two doublets by the lower symmetry of the tetragonal environment of the