CaPtAs: A new noncentrosymmetric superconductor

We report the discovery of a new noncentrosymmetric superconductor CaPtAs. It crystallizes in a tetragonal structure (space group I4₁md, No. 109), featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis (a = b = 4.18 Å, and c = 43.70 Å). The superconductivity of CaPtAs with T_c = 1.47 K was characterized by means of electrical resistivity, specific heat, and ac magnetic susceptibility. The electronic specific heat C_e(T)/T shows evidence for a deviation from the behavior of a conventional BCS superconductor, and can be reasonably fitted by a p-wave model. The upper critical field μ₀H_c2 of CaPtAs exhibits a moderate anisotropy, with an in-plane value of around 204 mT and an out-of-plane value of 148 mT. Density functional theory calculations indicate that the Pt-5d and As-4p orbitals mainly contribute to the density of states near the Fermi level, showing that the Pt-As honeycomb networks may significantly influence the superconducting properties.