Superconductivity in a new intermetallic structure type based on endohedral Ta@ i r7 G e4 clusters

We report the observation of superconductivity at a temperature near 3.5 K for the previously unreported compound TaIr2Ge2. In addition to being a superconductor, this material displays a new crystal structure type that contains endohedral clusters, as determined by single-crystal x-ray diffraction structure refinement; the structure is more complex than those of the commonly observed tetragonal 122 intermetallic phases. Despite the strong metal-metal interactions, electronic structure calculations show the presence of a relatively simple set of states at the Fermi level, consisting mostly of Ta atom orbital contributions. The superconducting transition is characterized by temperature-dependent resistivity, magnetic susceptibility and specific heat measurements, and is of the weak coupling BCS type with ΔC/γTc=1.55. The upper critical field at 0 K is estimated to be 2 T. Basic characterization of the superconductivity suggests that this material is similar to PbTaSe2, for which the effects of spin-orbit coupling may be important.