⁷⁵As-NQR Studies of Superconducting Filled Skutterudites PrRu₄As₁₂ and LaRu₄As₁₂

Abstract

We report ⁷⁵As nuclear quadrupole resonance (NQR) measurements of the filled skutterudite superconductors LaRu₄As₁₂ and PrRu₄As₁₂. The temperature dependence of the ⁷⁵As-NQR line and the nuclear spin–lattice relaxation rate 1⁄T₁ show that Pr³⁺ has a crystal electric field (CEF) singlet ground state with a separate first excited state. In the superconducting states of PrRu₄As₁₂ and LaRu₄As₁₂, 1⁄T₁ has a coherence peak just below the transition temperature and decreases exponentially at low temperatures. This behavior shows that the s-wave superconductivity occurs in both compounds.