Uranium-based heavy fermion

UPt3 belongs to the class of uranium-based heavy-fermion compounds. That classification is due to the large value for y in the expression for the specific heat at low temperature ... 

In most cases the low-temperature specific heat (at temperatures much lower than the Debye temperature) can be described by Cp = yT+ T, where yT is the so-called linear term due to the excitations of the conduction electrons, and is the low-temperature approximation of the specific heat of the lattice. For normal conductors, y is of the order of l-10mJ/(molK ), while heavy fermions show y-values up to 1000mJ/(molK ). Details about cerium- and uranium-based heavy-fermion materials have been reviewed by Grewe and Steglich (1991), Sereni (1991), Loewenhaupt and Fischer (1993), Fournier and Gratz (1993), Wachter (1994), Nieuwenhuys (1995), Onuki and Hasegawa (1995) and Arko et al. (1999). 

Introduction of Uranium-Based Heavy Fermion Superconductors... 

Prototypical heavy fermion systems are UBCij or UPtj. Photoemission studies have associated the uranium 5f contribution with the density of states in a narrow region at the Fermi level. This indicates only that there is a large density of states at p in a one-electron or band picture, subject to all of the interpretational problems of the 4f levels in Ce. Hence, photoemission shows the presence of a 5f photohole screened by conduction electrons that essentially reoccupy it during the photoemission process. All other many-body effects which give rise to the heavy-fermion ground state are broken by the photoemission process. Several other uranium-based heavy-fermion systems do not show an analogous narrow 5f-derived peak at the Fermi level. 

Since the discovery of the uranium-based heavy-fermion superconductors, it has been suspected that spin fluctuations are the pairing mechanism (Anderson 1984). Over the years, this belief has been re-enforced by the observations that followed in UPtj, UBei3, URu2Si2 and CeCu2Si2, and more recently in UNi2Al3 and UPd2Al3 ... 

During recent years it has become obvious that the properties of the so-called anomalous rare earth compounds (in particular cerium-based systems) show many similarities to the light-actinide (U, Np, Pu) compounds. The best known property which reflects the similarity is the appearance of heavy-fermion phenomena in many cerium and uranium intermetallics. 

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