Enhancement of T_c in CeIr(In_1-xCd_x)₅ studied by In-NQR

We report on superconducting nature under pressure in CeIr(In_1-xCd_x)₅ by In-Nuclear-Quadrupole-Resonance (NQR) studies. In CeIr(In_0.925Cd_0.075)₅, the inhomogeneous antiferromagnetic order at T_N ∼ 2.3 K is induced by Cd-dopants and superconductivity disappears at ambient pressure. However, the measurements of a nuclear-spin-lattice-relaxation rate 1/T₁ have revealed that the superconductivity suddenly occurs above 2.1 GPa. It is observed that the superconducting gap is enhanced in the Cd-doped sample, indicating that the Cd-doping induces the strong coupling superconductivity leading to the enhancement of T_c in the CeIrIn₅ system. Furthermore, we found that the residual density of states at the Fermi level increases with increasing pressure, suggesting that the superconducting nature of CeIrIn₅ is quite different from those of CeCoIn₅ and CeRhIn₅.