Abstract
We report on a systematic study of the superconducting characteristics and Pr crystalline-electric-field (CEF) levels of the filled skutterudite PrRu 4 As 12 ( T c = 2.33 K). The temperature dependences of the upper critical field H c2 and the Ginzburg–Landau (Maki) parameter κ 2 suggest s -wave clean-limit superconductivity. The electronic specific heat coefficient γ∼95 mJ/(K 2 ·mol), which is ∼1.5 times larger than that of LaRu 4 As 12 , indicates 4 f -originating quasiparticle mass enhancement. The magnetic susceptibility χ( T ) indicates that the CEF ground state is a Γ 1 singlet and a Γ 4 (1) triplet first excited state lies at Δ CEF ∼30 K above. A systematic comparison among PrOs 4 Sb 12 , PrRu 4 Sb 12 , PrRu 4 As 12 , and La-based reference compounds suggests that the inelastic exchange scattering and aspherical charge scattering of conduction electrons from CEF-split 4 f levels play an essential role in the quasiparticle mass enhancement and in determining the value of T c in the Pr-based filled skutterudites.
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