Probing the superconducting gap symmetry of PrOs$_{4}$Sb$_{12}$: A penetration depth study

TL;DR

This study investigates the superconducting gap symmetry of PrOs$_{4}$Sb$_{12}$ by measuring the magnetic penetration depth at very low temperatures, revealing a power-law behavior indicative of point nodes and supporting a strong-coupling, unconventional superconducting state.

Contribution

The paper provides the first detailed penetration depth measurements of PrOs$_{4}$Sb$_{12}$, identifying a specific gap structure consistent with a multidomain, point-node superconductor with strong coupling.

Findings

Penetration depth follows a $ extit{T}^2$ power law at low temperatures.

Data best fits a $^{3}$He A-phase-like gap with two point nodes.

PrOs$_{4}$Sb$_{12}$ is a strong-coupling superconductor with two point nodes.

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, $\lambda \sim \mathit{T}^{2}, \rho_{s} \sim \mathit{T}% ^{2}$ 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.