Anisotropic Magnetic Fluctuations and Unconventional Superconductivity in the Layered Heavy Fermion Compound CeIrIn5

We report the 115 In nuclear spin–lattice relaxation rate (1/ T 1 ) measurements down to 90 mK in the new heavy fermion (HF) compound CeIrIn 5 . At 0.4 K ≤ T ≤100 K, 1/ T 1 is strongly T -dependent, which indicates that the 4f electrons are much more itinerant than in known Ce-based HFs. From the unique temperature variation of 1/ T 1 T , we find that this compound is located near a quantum critical point, with anisotropic spin fluctuations due to a layered crystal structure. Below the bulk superconductivity temperature 0.40 K, 1/ T 1 follows a T 3 variation without a coherence peak, which indicates unconventional superconductivity with line-node gap. These aspects are reminiscent of the high- T c copper oxides and suggest the importance of the magnetic fluctuations for the occurrence of the unconventional superconductivity.