Twenty-five years of heavy-fermion superconductivity

We discuss first the physical properties of the prototypical heavy-fermion superconductor CeCu2Si2 and, second, the relationship of its superconductivity with both a spin-density-wave-type quantum phase transition and a weak valence transition of Ce that occurs at high pressure. We, then, briefly address the isostructural heavy-fermion compound YbRh2Si2, displaying a local type of quantum critical behavior which appears to be detrimental to superconductivity