NORMAL AND SUPERCONDUCTING PHASES OF HEAVY FERMIONS

A review of recent experimental findings in the field of heavy fermions is given, with an emphasis on the three types of transition encountered: antiferromagnetic, metamagnetic and superconducting. The appearance of long-range antiferromagnetic ordering of small moments in compounds such as URu2Si2 and UPt3 is described in terms of its structure and observable consequences. A comparison is made between the behaviour of CeRu2Si2 and that of UPt3 below and above their magnetic field-induced transitions to a polarised state, drawing upon the detailed information now available from Fermi-surface studies, and from neutron scattering, specific heat and magnetoresistance measurements. Finally, the rapidly growing evidence for a multiplicity of superconducting phases in UPt3 is discussed, in parallel with the related case of Th-doped UBe13. The issue of a possible coupling between superconducting and antiferromagnetic order parameters is addressed.