CeIrIn 5: Superconductivity on a magnetic instability

We report on the doping-induced antiferromagnetic state and Fermi-liquid state that are connected by a superconducting region in a series of CeIrIn5-xHgx, CeIrIn5-xSnx, and CeIr1-xPtxIn5 single crystals. Measurements of the specific heat C(T) and electrical resistivity ρ(T) demonstrate that hole doping via Hg/In substitution gives rise to an antiferromagnetic ground state, but substitutions of In by Sn or Ir by Pt (electron doping) favor a paramagnetic Fermi-liquid state. A conelike non-Fermi-liquid region is observed near CeIrIn5, showing a diverging effective mass on the slightly Hg-doped side. The obtained temperature-doping phase diagram suggests that CeIrIn5 is in proximity to an antiferromagnetic quantum critical point, and heavy fermion superconductivity in this compound is mediated by magnetic quantum fluctuations rather than by valence fluctuations.