Superconducting properties of Pr-based Filled skutterudite PrRu${}_4$As${}_{12}$

Abstract

We report on systematic study of superconducting characteristics and Pr crystalline-electric-field (CEF) levels of filled-skutterudite \pra ($T_{\mathrm{c}}$ = 2.33 K). The temperature dependences of the upper critical field $H_{c2}$ and the Ginzburg-Landau (Maki) parameter $\hat{I}{º}_2$ suggest an s-wave clean-limit superconductivity. The electronic specific heat coefficient ${\hat{I}}^3\sim 95$ mJ/K${}^2$mol, being $\sim 1.5$ times larger than that for \lra, indicates $4f$-originating quasiparticle mass enhancement. Magnetic susceptibility $\ddot{I}‡(T)$ indicates that the CEF ground state is a $\hat{I}{“}_1$ singlet and a $\hat{I}{“}_4^{(1)}$ triplet first excited state lies at $\hat{I}{”}_{\mathrm{CEF}}\sim 30$ K above. Systematic comparison among \pos, \prs, \pra and La-based reference compounds suggests that inelastic exchange- and aspherical-charge-scatterings of conduction electrons from CEF-split $4f$ levels play an essential role for the quasiparticle mass enhancement and the value of $T_{\mathrm{c}}$ in the Pr-based filled skutterudites.

4 pages, 6 figures