We have investigated the bulk and microscopic properties of the rhombohedral intermediate valence superconductor CeIr3 by employing magnetization, heat capacity, and muon spin rotation and relaxation (μSR) measurements. The magnetic susceptibility indicates bulk superconductivity below TC=3.1K. Heat capacity data also reveal a bulk superconducting transition at 3.1 K with a second weak anomaly near 1.6 K. Zero-field μSR data show no strong evidence of broken time-reversal symmetry but support the presence of spin fluctuations below TC. Transverse-field μSR measurements suggest a fully gapped, isotropic, s-wave superconductivity with 2Δ(0)/kBTC=3.76(3), very close to 3.53, the Bardeen-Cooper-Schrieffer gap value for weak-coupling superconductors. From the temperature variation of the magnetic penetration depth, we have also determined the London penetration depth λL(0)=435(2)nm, the carrier effective-mass enhancement m∗=1.69(1)me, and the superconducting carrier density ns=2.5(1)×1027 carriers m-3. The fact that LaIr3, with no 4f electrons, and CeIr3 with 4fn electrons where n≤1 (Ce ion in a valence fluctuating state), both exhibit the same s-wave gap symmetry indicates that the Ir-d band governs the physics of these two compounds near the Fermi level, which is in agreement with previous band structure calculations.
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