Crystallographic and superconducting properties of the fully gapped noncentrosymmetric 5d-electron superconductors CaMSi₃ (M= Ir, Pt)

We report crystallographic, specific heat, transport, and magnetic properties of the recently discovered noncentrosymmetric 5d-electron superconductors CaIrSi₃ (T_c=3.6 K) and CaPtSi₃ (T_c=2.3 K). The specific heat suggests that these superconductors are fully gapped. The upper critical fields are less than 1 T, consistent with limitation by conventional orbital depairing. High, non-Pauli-limited μ₀H_c2 values, often taken as a key signature of novel noncentrosymmetric physics, are not observed in these materials because the high carrier masses required to suppress orbital depairing and reveal the violated Pauli limit are not present.