Probing the superconducting gap symmetry of PrRu$_{4}$Sb$_{12}$: A comparison with PrOs$_{4}$Sb$_{12}$

Abstract

We report measurements of the magnetic penetration depth $λ$ in single crystals of PrRu$_{4}$Sb$_{12}$ down to 0.1 K. Both $λ$ and superfluid density $ρ_{s}$ exhibit an exponential behavior for $T$ $<$ 0.5$T_{c}$, with parameters $Δ$(0)/\textit{k}$_{B}$\textit{T}$_{c}$ = 1.9 and $λ(0)$ = 2900 Å. The value of $Δ$(0) is consistent with the specific-heat jump value of $ΔC/γT_{c}$ = 1.87 measured elsewhere, while the value of $λ(0)$ is consistent with the measured value of the electronic heat-capacity coefficient $γ$. Our data are consistent with PrRu$_{4}$Sb$_{12}$ being a moderate-coupling, fully-gapped superconductor. We suggest experiments to study how the nature of the superconducting state evolves with increasing Ru substitution for Os.