Heavy-fermion superconductivity: Experimental status report

New observations are reported for the heavy-fermion superconductors CeCu 2Si 2, UBe 13 and UPt 3. These results are discussed with respect to the following issues: (i) the competition between different cooperative phenomena in CeCu 2Si 2; (ii) the question whether the whole Fermi surface contributes to the superconducting transition in the three compounds; (iii) the nature of the superconducting order parameter. Taking into account more published data for these systems, the author can delineate the present status of the field: CeCu 2Si 2 behaves as a singlet superconductor with possibly anisotropic Cooper pairing. UPt 3 appears to possess an anisotropic order parameter, either of the singlet or triplet type. No definite conclusions can yet be drawn for UBe 13, mainly because its superconducting properties are severely modified by field and temperature dependences of the normal-state parameters