Phenomenology of Heavy Fermion Systems

Local heavy fermions are formed at the sites of independent Kondo ions as substantiated by the discovery of a pronounced low temperature anomaly in the thermal expansion of certain dilute and moderately concentrated Ce alloys. In periodic Kondo lattice systems like CeAl3 a coherent heavy fermion band structure is developed at low T, one hallmark of which is a maximum in the Sommerfeld coefficient γ(T) near 0.4 K. This distinct phenomenon can even show up in the presence of long-range magnetic order as in CeCu2Ge2 and is found to have a strong influence on the superconducting properties of CeCu2Si2. According to its normal-state behavior, UBe13 appears to be closely related to the Ce-based Kondo lattices. A number of the superconducting properties of pure and Th-doped UBe13 can be well understood in terms of an anisotropic pairing interaction, which seems to track the anisotropy of the Fermi surface. This leads to a reinterpretation of the phase diagram of the superconducting states in U1-xThxBe13