Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs$_{4}$Sb$_{12}$: Sb-NQR Study

TL;DR

This study uses Sb-NQR measurements in filled skutterudite superconductors to investigate how impurities affect the gap function, revealing the presence of nodes in PrOs$_{4}$Sb$_{12}$'s superconducting gap.

Contribution

It provides experimental evidence that impurity-induced states suggest nodal structures in the superconducting gap of PrOs$_{4}$Sb$_{12}$, advancing understanding of its pairing symmetry.

Findings

Impurity substitution increases low-temperature relaxation rate.

Finite density of states appears at the Fermi level due to impurities.

Results imply the presence of nodes in the superconducting gap.

Abstract

We have carried out nuclear quadrupole resonance (NQR) measurements in the filled skutterudite compounds Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ ($x=0.1, 0.2$), in order to gain insights into the symmetry of the superconducting gap function. Upon replacing Os with Ru, the spin-lattice relaxation rate $1/T_1$ becomes proportional to temperature ($T$) at low $T$ far below $T_c$, and the magnitude of $(1/T_1T)_{low-T}$ increases with increasing Ru content. These results indicate that a finite density of states is induced at the Fermi level by the impurity, and thus suggest that there exist nodes in the gap function of PrOs$_{4}$Sb$_{12}$.