Superconductivity and spin fluctuations in the actinoid-platinum metal borides {Th, U} Pt sub(3) B

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2015-07, Vol.92 (2)
• Main Authors: Bauer, E, Royanian, E, Michor, H, Sologub, O, Scheidt, E-W, Goncalves, A P, Bursik, J, Wolf, W, Reith, D, Blaas-Schenner, C, Moser, R, Podloucky, R, Rogl, P
• Format: Article
• Language: English
• Subjects: Compensation; Condensed matter; Crystal structure; Electrical resistivity; Fluctuation; Formations; Superconductivity; Vacancies
• ISSN: 1098-0121; 1550-235X

Investigating the phase relations of the system {Th, U}-Pt-B at 900[degrees]C the formation of two compounds has been observed: cubic ThPt sub(3) B with Pm3m structure as a representative of the perovskites, and tetragonal UPt sub(3) B with P4mm structure being isotypic to the noncentrosymmetric structure of CePt sub(3) B. The crystal structures of the two compounds are defined by combined x-ray diffraction and transmission electron microscopy. Characterization of physical properties for ThPt sub(3) B reveals a superconducting transition at 0.75 K and an upper critical field at T = 0 exceeding 0.4 T. For nonsuperconducting UPt sub(3) B a metallic resistivity behavior was found in the entire temperature range; at very low temperatures spin fluctuations become evident and the resistivity [rho](T) follows non-Fermi liquid characteristics, [rho] = [rho] sub(0) + AT super(n)with n = 1.6. Density functional theory (DFT) calculations were performed for both compounds for both types of structures. They predict that the experimentally claimed cubic structure of ThPt sub(3) B is thermodynamically not stable in comparison to a tetragonal phase, with a very large enthalpy difference of 25 kJ/mol, which cannot be explained by the formation energy of B vacancies. However, the presence of random boron vacancies possibly stabilizes the cubic structure via a local strain compensation mechanism during the growth of the crystal. For UPt sub(3) B the DFT results agree well with the experimental findings.