Low-Temperature Chiral Crystal Structure and Superconductivity in (Pt 0.2 Ir 0.8 ) 3 Zr 5 .

We report the observation of superconductivity in (Pt 0.2 Ir 0.8 ) 3 Zr 5 with a chiral space group ( P 6 1 22) at low temperatures. The bulk nature of the superconductivity at a transition temperature of 2.2 K was confirmed using specific heat measurements. We revealed that (Pt 0.2 Ir 0.8 ) 3 Zr 5 obeys the weak-coupling Bardeen-Cooper-Schrieffer model, and the dominant mechanism in the upper critical field is the orbital pair-breaking limit rather than the Pauli-Clogston limit. This indicates that the antisymmetric spin-orbit coupling caused by the chiral crystal structure does not significantly affect the superconductivity of (Pt 0.2 Ir 0.8 ) 3 Zr 5 .