Pairing symmetry of an intermediate valence superconductor CeIr3 investigated using μSR measurements

We have investigated the bulk and microscopic properties of the rhombohedral intermediate valence superconductor ${\mathrm{CeIr}}₃$ by employing magnetization, heat capacity, and muon spin rotation and relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements. The magnetic susceptibility indicates bulk superconductivity below ${T}_{\mathrm{C}}=3.1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Heat capacity data also reveal a bulk superconducting transition at 3.1 K with a second weak anomaly near 1.6 K. Zero-field $\ensuremath{\mu}\mathrm{SR}$ data show no strong evidence of broken time-reversal symmetry but support the presence of spin fluctuations below ${T}_{\mathrm{C}}$. Transverse-field $\ensuremath{\mu}\mathrm{SR}$ measurements suggest a fully gapped, isotropic, $s$-wave superconductivity with $2\mathrm{\ensuremath{\Delta}}(0)/{k}_{\mathrm{B}}{T}_{\mathrm{C}}=3.76(3)$, 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 ${\ensuremath{\lambda}}_{\mathrm{L}}(0)=435(2)\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, the carrier effective-mass enhancement ${m}^*=1.69(1){m}_{\mathrm{e}}$, and the superconducting carrier density ${n}_{\mathrm{s}}=2.5(1)\ifmmode\times\else\texttimes\fi{}{10}²⁷$ carriers ${\mathrm{m}}^{\ensuremath{-}3}$. The fact that ${\mathrm{LaIr}}₃$, with no $4f$ electrons, and ${\mathrm{CeIr}}₃$ with $4{f}ⁿ$ electrons where $n\ensuremath{\le}1$ (Ce ion in a valence fluctuating state), both exhibit the same $s$-wave gap symmetry indicates that the $\mathrm{Ir}\text{\ensuremath{-}}d$ band governs the physics of these two compounds near the Fermi level, which is in agreement with previous band structure calculations.