Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs₄Sb₁₂: Sb-NQR Study

Abstract

We have carried out nuclear quadrupole resonance (NQR) measurements in the filled skutterudite compounds Pr(Os1−xRux)4Sb12 (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/T1 becomes proportional to temperature (T) at low T far below Tc, and the magnitude of (1/T1T)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 PrOs4Sb12.