Superconductivity in CaBi2

Abstract

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.