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

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Abstract
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. The authors use a slave-boson treatment of the f2-f3 Anderson lattice to compute thermodynamic quantities including the Wilson ratio. The authors 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. They show that the charge fluctuations are greatly suppressed relative to the spin fluctuations even for nf approximately 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.