Normal-state and superconducting properties of the cubic Laves phase ThIr2

Abstract

The physical properties of the cubic Laves phase superconductor ThIr2 have been studied by resistivity, magnetic susceptibility and thermodynamic measurements. This compound is found to be a weak coupling type-II superconductor with a Tc of 5.58 K and a fully isotropic superconducting gap. The electronic specific heat coefficient, upper critical field and Ginzburg-Laudau parameter are determined to be 13.1 mJ mol−1 K−2, 2.25 T, and 20.4, respectively. In the normal state, the susceptibility follows a Curie-Weiss behavior with a paramagnetic moment of 0.46 μB per f.u.. Furthermore, the low-temperature resistivity exhibits a quadratic temperature dependence, yielding a large Kadowaki-Woods ratio of 7.6×10−5μΩ cm/(mJ mol−1 K−1)2. This, together with a Wilson ratio of ~1.4, suggests the importance of electronic correlation in ThIr2. First-principles calculations show that the valence band states below the Fermi level are dominated by the Ir-5d orbitals, yet significant hybridizations with the Ir-6p, Th-6d, 7p orbits are detected at the Fermi level. The inclusion of spin-orbit coupling has little influence on the Fermi surface shape but lowers the density of states toward the experimental value. A comparison with isostructural CaIr2 and SrIr2 is also presented.