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

Abstract

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 ($\hat{I}¼$SR) measurements. The magnetic susceptibility indicates bulk superconductivity below $T_{\mathrm{C}}=3.1$~K. Heat capacity data also reveal a bulk superconducting transition at $T_{\mathrm{C}}=3.1$~K with a second weak anomaly near 1.6~K. At $T_{\mathrm{C}}$, the jump in heat capacity $\hat{I}”C$/${\hat{I}}^3{T}_{\mathrm{C}}\sim 1.39(1)$, is slightly less than the BCS weak coupling limit of 1.43. Transverse-field $\hat{I}¼$SR measurements suggest a fully gapped, isotropic, $s$-wave superconductivity with 2$\hat{I}”(0)/k_{\mathrm{B}}{T}_{\mathrm{C}}=3.76(3)$, 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 $\hat{I}{»}_{\mathrm{L}}(0)=435(2)$~nm, the carriers' effective mass enhancement $m^{\ast }=1.69(1)m_{\mathrm{e}}$ and the superconducting carrier density $n_{\mathrm{s}}=2.5(1)\times 10^{26}$ carriers m${}^{-3}$. The fact that LaIr${}_3$, with no $4f$-electrons, and CeIr${}_3$ with $4f^n$ electrons where $n\le 1$-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.

8 pages 4 figures