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Abstract:
The Cooper pairs in the superconductors CeCu 2Si 2, UBe 13, UPt 3, and
URu 2Si 2 are formed by quasiparticles with effective mass m* of order
100 m el. m* originates in very strong correlations between f-electrons
which become weakly delocalized well below a characteristic temperature
T*~5-50 K via a Kondo-type mechanism. These `heavy fermions' dominate
the low-temperature properties of a number of lanthanide- and
actinide-based compounds, spanning the full range between coherent Fermi
liquid, band magnetism and superconductivity. The pairing interaction in
the `heavy-fermion superconductors' is likely to differ from the
BCS-type phonon-mediated coupling. In addition, their order parameters
appear to be highly anisotropic. Most of the experimental evidence
points to even-parity (`singlet') rather than odd-parity (`triplet')
pairing.
