Probing the superconducting gap symmetry of PrOs${}_4$Sb${}_{12}$: A penetration depth study

Abstract

We report measurements of the magnetic penetration depth $\lambda$ in single crystals of PrOs${}_4$Sb${}_{12}$ down to $\sim$0.1 K using a tunnel-diode based, self-inductive technique at 21 MHz, with the ac field applied along the \textit{a}, \textit{b} and \textit{c} directions. In all three field orientations the penetration depth and superfluid density ${\rho }_s$ tend to follow a power law, $\lambda \sim T^2,{\rho }_s\sim T$ at low temperatures. ${\rho }_s$ for various gap functions have been calculated, and data is best fit by the ${}^3$He A-phase-like gap with multidomains, each having two point nodes along a cube axis, and parameter ${\Delta }_0$(0)/\textit{k}${}_B$\textit{T}${}_c$ = 2.6. This suggests that PrOs${}_4$Sb${}_{12}$ is a strong-coupling superconductor with two point nodes on the Fermi surface. We also confirm the observation of the double transitions at 1.75 K and 1.85 K seen in other measurements.