Superconductivity in CaBi₂

Superconductivity is observed with critical temperature T_c = 2.0 K in self-flux-grown single crystals of CaBi₂. This material adopts the ZrSi₂ structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi₂ were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at T_c is ΔC/γT_c = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol^-1 K^-2 and the Debye temperature Θ_D = 157 K. The electron-phonon coupling strength is λ_el-ph = 0.59, and the thermodynamic critical field H_c is low, between 111 and 124 Oe CaBi₂ is a moderate coupling type-I superconductor. Results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin-orbit coupling and electronic property anisotropy. We find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.