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Zusammenfassung:
Unconventional superconductivity in non-centrosymmetric superconductors has attracted a considerable amount of attention. While several lanthanide-based materials have been reported previously, the number of actinide-based systems remains small. In this work, we present the discovery of a novel cubic complex non-centrosymmetric superconductor Th4Be33Pt16 (I (4) over bar 3d space group). This intermetallic cage compound displays superconductivity below T-c = 0.90 +/- 0.04 K, as evidenced by specific heat and resistivity data. Th4Be33Pt16 is a type-II superconductor, which has an upper critical field H-c2 = 0.27 T and a moderate Sommerfeld coefficient gamma(n) = 16.3 +/- 0.8 mJ mol(Th)(-1) K-2. A non-zero density of states at the Fermi level is evident from metallic behavior in the normal state, as well as from electronic band structure calculations. The isostructural U4Be33Pt16 compound is a paramagnet with a moderately enhanced electronic mass, as indicated by the electronic specific heat coefficient gamma(n) = 200 mJ mol(U)(-1)K(-2) and Kadowaki-Woods ratio A/gamma(2) = 1.1 x 10(-5) mu Omega cm K-2 mol(U)(2)(mJ)(-2). Both Th4Be33Pt16 and U4Be33Pt16 are crystallographically complex, each hosting 212 atoms per unit cell.
