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

We have investigated the bulk and microscopic properties of the rhombohedral intermediate valence superconductor CeIr${}_3$ by employing magnetization, heat capacity, and muon spin rotation and relaxation ($\mu$SR) measurements. The magnetic susceptibility indicates bulk superconductivity below $T_$\mathrm{C}$ = 3.1$K\mathrm{.}Heatcapacitydataalsorevealabulksuperconductingtransitionat$T_$\mathrm{C}$ = 3.1$Kwithasecondweakanomalynear1.6K\mathrm{.}At$T_{$\mathrm{C}$}$,thejumpinheatcapacity$\Delta C$\mathrm{/}$\gamma T_{$\mathrm{C}$} \sim 1.39(1)$, is slightly less than the BCS weak coupling limit of 1.43. Transverse-field $\mu$SR measurements suggest a fully gapped, isotropic, $s$-wave superconductivity with 2$\Delta(0)/k_{$\mathrm{B}$}T_{$\mathrm{C}$} = 3.76(3)$, very close to 3.56, the BCS gap value for weak-coupling superconductors. From the temperature variation of magnetic penetration depth, we have also determined the London penetration depth $\lambda_{$\mathrm{L}$}(0) = 435(2)$nm,thecarrier{s}^{\mathrm{\prime }}effectivemassenhancement$m^{*} = 1.69(1)m_{$\mathrm{e}$}$andthesuperconductingcarrierdensity$n_{$\mathrm{s}$} = 2.5(1)\times 10^{26}$carriersm$^{-3}$\mathrm{.}ThefactthatLaIr$_3$,withno$4f$-electrons,andCeIr$_3$with$4f^{n}$electronswhere$n \le 1$-electron (Ce ion in a valence fluctuating state), both exhibit the same $s$-wave gap symmetry indicates that the physics of these two compounds is governed by the Ir-$d$ band near the Fermi-level, which is in agreement with previous band structure calculations.