Comprehensive Macroscopic Investigation on Hexagonal C14 Laves-Type Ru-Based Superconductors ARu

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We discovered that LuRu<inf>2</inf>with a hexagonal C14 Laves phase structure exhibited a superconducting transition at 2.23 K. The magnetization, electronic resistivity, and specific heat measurements for LuRu<inf>2</inf>and the C14 Laves phases YRu<inf>2</inf>and ScRu<inf>2</inf>, superconductors with the same number of valence electrons, reveal that the compounds are type-II weak-coupling BCS superconductors with nodeless but probably slightly anisotropic superconducting gaps. A noteworthy finding of these experiments is that the compounds are correlated electron systems, as suggested by their Wilson ratios of approximately 2 and the large enhancement in their electronic specific heat coefficients compared with those obtained by GGA calculation. Many Ru-containing compounds show correlated electron phenomena, but they are the first examples of a Ru-based correlated electron system with neither nonmetallic nor metalloid elements as constituent elements, probably owing to the covalent bond character of Ru peculiar to Laves phases. The relationships among the superconducting transition temperatures, Debye temperatures, and electronic specific heat coefficients of ARu<inf>2</inf>(A = Lu, Y, Sc) clearly demonstrated the phonon-mediated superconductivity of the compounds.
2013-12-15