Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs${}_4$Sb${}_{12}$: Sb-NQR Study

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 $(1/T_{1}T{)}_{low-T}$ 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${}_{12}$.

10 pages, with 6 figures