Non-centrosymmetric superconductor Th 4 Be 33 Pt 16 and heavy-fermion U 4 Be 33 Pt 16 cage compounds

Abstract

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 Th 4Be 33Pt 16 (I4 ¯ 3 d space group). This intermetallic cage compound displays superconductivity below Tc= 0.90 ± 0.04 K, as evidenced by specific heat and resistivity data. Th 4Be 33Pt 16 is a type-II superconductor, which has an upper critical field H c 2= 0.27 T and a moderate Sommerfeld coefficient γn= 16.3 ± 0.8 mJ molTh-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 U 4Be 33Pt 16 compound is a paramagnet with a moderately enhanced electronic mass, as indicated by the electronic specific heat coefficient γn= 200 mJ molU-1 K - 2 and Kadowaki–Woods ratio A/ γ2= 1.1 × 10 - 5 μ Ω cm K 2molU2 (mJ)- 2. Both Th 4Be 33Pt 16 and U 4Be 33Pt 16 are crystallographically complex, each hosting 212 atoms per unit cell.