Magnetic Response Of Strongly Correlated Electron Systems

R. Osborn; in collaboration with M. R. Norman, Condensed Matter Theory Group, and J. C. Campuzano, Synchrotron Radiation Studies Group

The work on strongly correlated systems has concentrated on understanding the origin of the unusual bulk properties of non-Fermi liquid uranium compounds. We have now performed neutron measurements using full polarization analysis of a compound with x = 2.  In previous years, we have established the existence of universal scaling of the dynamic magnetic susceptibility of f-electrons in the non-Fermi liquid compounds UCu5-xPdx that we attributed to quantum critical scattering. Exploiting the "negative chemical pressure" produced by doping CeAl3 with lanthanum is providing new insights into puzzling low-temperature anomalies in this canonical heavy fermion compound.

Localization of f-electrons at a Quantum Critical Point.  In previous years, we have established the existence of universal scaling of the dynamic magnetic susceptibility of f-electrons in the non-Fermi liquid compounds UCu5-xPdx (x = 1, 1.5), which we attributed to quantum critical scattering.  We have now performed neutron measurements using full polarization analysis of a compound with x = 2.  With increasing palladium concentration, the lattice expands and there is a phase transition to a spin glass phase just below x = 2.  There is a dramatic change in the nature of the magnetic response at this composition.  At low temperatures, the response is confined to very low frequencies, and but becomes much broader with increasing temperature.  This is in contrast to the x = 1 and 1.5 results, which showed that the energy scale of the magnetic response follows a power law with no temperature dependence up to 300K in energy loss.

Evidence for the Anisotropic Kondo Model in Ce1-xLaxAl3.  Exploiting the "negative chemical pressure" produced by doping CeAl3 with lanthanum is providing new insights into puzzling low-temperature anomalies in this canonical heavy fermion compound.  It was recently shown that an unexplained peak in the specific heat increases from ~0.5 K at x = 0 to 2.2 K at x = 0.2.  Our neutron measurements on Ce0.8La0.2Al3 have shown that the magnetic response becomes quasielastic below 2K.  However, there is no evidence from high-intensity powder diffraction of magnetic ordering.  Instead, we have shown that the behavior can be modeled in terms of the anisotropic Kondo effect, showing that the transition is driven by the decreased dissipation of the single-ion dynamics rather than cooperative magnetic order.