Superconductivity in Rh 2 Ga 9 and Ir 2 Ga 9 without Inversion Symmetry

Superconductivity with Tc 2 K was discovered in the intermetallic binary compounds Rh₂Ga₉ and Ir₂Ga₉. This is the first observation of superconductivity in the Rh-Ga and Ir-Ga binary systems. Both compounds crystallize in a distorted Co₂Al₉-type structure (monoclinic, space group: $Pc$), which lacks spatial inversion symmetry. Specific heat measurements revealed that both compounds are weak-coupling BCS superconductors having an isotropic superconducting gap. Measurements in magnetic fields indicated type-I superconductivity with a critical field Hc(0) 130 Oe for Rh₂Ga₉ and type-II superconductivity with an upper critical field Hc2(0) 250 Oe for Ir₂Ga₉.