Superconductivity in Alkaline Earth Metal-Filled Skutterudites BaIrX (X = As, P).

We report superconductive iridium pnictides BaIrX (X = As and P) with a filled skutterudite structure, demonstrating that Ba filling dramatically alters their electronic properties and induces a nonmetal-to-metal transition with increasing the Ba content x. The highest superconducting transition temperatures are 4.8 and 5.6 K observed for BaIrAs and BaIrP, respectively. The superconductivity in BaIrX can be classified into the Bardeen-Cooper-Schrieffer type with intermediate coupling.