Electronic band structure, specific heat, andP195tNMR studies of the filled skutterudite superconductorThPt4Ge12

Abstract

Specific-heat measurements and $^{195}\text{P}\text{t}$ NMR studies have been carried out for actinoid-bearing filled skutterudite superconductor ${\text{ThPt}}_{4}{\text{Ge}}_{12}$ with ${T}_{c}=4.62\text{ }\text{K}$. The lattice contribution to the total specific heat has been analyzed in terms of combination of the Einstein and Debye theories. The data show that ${\text{ThPt}}_{4}{\text{Ge}}_{12}$ has one optical and two acoustic vibrational modes. The numbers of such modes and the magnitudes of the vibration frequencies suggest that the two acoustic modes can be attributed to the Pt and Ge atoms forming two different cages in the cubic bcc skutterudite structure, while the optical mode can be associated with weakly bonded Th atoms occupying a center of these cages. The $^{195}\text{P}\text{t}$ Knight shift and spin-lattice relaxation rates in ${\text{ThPt}}_{4}{\text{Ge}}_{12}$ can be understood in terms of conventional Fermi-liquid picture. Distinct anisotropy in these quantities presumably arises from $d(p)$-orbital components. The experimental data have been confronted with the electronic band structure of ${\text{ThPt}}_{4}{\text{Ge}}_{12}$ calculated by ab initio full-potential relativistic local-orbital method within the local-density approximation. Enhanced value of the mass enhancement coefficient points to considerable electron-phonon interaction and some electron-electron correlations. The Fermi surface of metallic ${\text{ThPt}}_{4}{\text{Ge}}_{12}$ consists of nonspherical hole and electron sheets.