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 UPd2Al3 and by valence fluctuations in pressurized CeCu2Si2. Moreover, evidence from inelastic neutron scattering for HF superconductivity being mediated by quantum critical spin-density-wave fluctuations in CeCu2Si2 is discussed.