Mixed-valence and Kondo lattice behaviour in the uranium heavy-fermion systems

The uranium heavy-fermion systems exhibit 'Kondo-like' behaviour even though the valence, nf, is non-integral. Their low-temperature properties are characterised by a single small energy scale, TK. We use a slave-boson treatment of the f2-f3 Anderson lattice to compute thermodynamic quantities including the Wilson ratio. We compute the frequency and energy-dependent charge and spin susceptibilities and show that at low temperature these have a Fermi-liquid form with a greatly enhanced electron mass. We show that the charge fluctuations are greatly suppressed relative to the spin fluctuations even for nf ∼ 2.5 indicating that the spin fluctuations dominate the behaviour throughout the mixed-valence regime. Quasiparticle interactions are described by fluctuations in the boson fields about their mean-field values. To O(1/N) the interaction is due to charge fluctuations and gives rise to d-wave superconductivity. Corrections of O(1/N2) are due to spin fluctuations. These change the results substantially and p-wave superconductivity may also be obtained. (author)