Experimental evidence for unconventional BCS states in heavy-fermion metals

A variety of unconventional pairing mechanisms seem to be operating in heavy-fermion superconductors. We address briefly Cooper pairing mediated by magnetic excitons in UPd 2 Al 3 and by valence fluctuations in pressurized CeCu 2 Si 2 . Moreover, evidence from inelastic neutron scattering for HF superconductivity being mediated by quantum critical spin-density-wave fluctuations in CeCu 2 Si 2 is discussed.