Superconducting Properties of Pr-Based Filled Skutterudite PrRu₄As₁₂

抄録

We report on a systematic study of the superconducting characteristics and Pr crystalline-electric-field (CEF) levels of the filled skutterudite PrRu₄As₁₂ (T_c=2.33 K). The temperature dependences of the upper critical field H_c2 and the Ginzburg–Landau (Maki) parameter κ₂ suggest s-wave clean-limit superconductivity. The electronic specific heat coefficient γ∼95 mJ/(K²·mol), which is ∼1.5 times larger than that of LaRu₄As₁₂, indicates 4f-originating quasiparticle mass enhancement. The magnetic susceptibility χ(T) indicates that the CEF ground state is a Γ₁ singlet and a Γ₄⁽¹⁾ triplet first excited state lies at Δ_CEF∼30 K above. A systematic comparison among PrOs₄Sb₁₂, PrRu₄Sb₁₂, PrRu₄As₁₂, and La-based reference compounds suggests that the inelastic exchange scattering and aspherical charge scattering of conduction electrons from CEF-split 4f levels play an essential role in the quasiparticle mass enhancement and in determining the value of T_c in the Pr-based filled skutterudites.