The first heavy fermion superconductor, CeCu₂Si₂, was discovered by Frank Steglich in 1978 with a critical temperature of 0.7 K.
Over 30 heavy fermion superconductors are known in Ce- and U-based intermetallics, from UPt₃ (0.48 K) and UBe₁₃ (0.85 K, reported by H. R. Ott and colleagues in 1983) up to PuCoGa₅ at 18.5 K, found in 2002 by a team including Sarrao and J. D. Thompson.
Their f-electrons hybridize with conduction electrons into heavy quasiparticles that themselves form the Cooper pairs, defying description by BCS theory.