Unconventional superconductivity in f-electron systems

We report pressure-induced superconductivity in antiferromagnetic cerium compounds and a ferromagnetic uranium compound, focusing on the relation between the superconducting state and the Fermi surface instability in CeRhIn ₅ and the huge upper critical field H_c2 in CeIrSi ₃ without inversion symmetry in the crystal structure. The pairing interaction is well correlated with ferromagnetism, as well as antiferromagnetism or antiferromagnetic fluctuations. In the recently discovered superconductor NpPd₅Al₂, superconductivity is found to be located in the vicinity of an antiferromagnetically ordered state. The upper critical field H_c2 is strongly supressed by the large paramagneic effect, and the corresponding magnetization curve indicates a step-like increase at H_c2, producing a first-order phase transition.