Superconductivity in CaBi$_{2}$

TL;DR

This paper reports the discovery of superconductivity at 2.0 K in CaBi₂, a layered material with a ZrSi₂ structure, characterized through various measurements and electronic structure calculations.

Contribution

The study provides the first detailed characterization of superconductivity in CaBi₂, including experimental measurements and electronic structure analysis highlighting its moderate coupling and layered electronic properties.

Findings

Superconductivity observed at T_c = 2.0 K in CaBi₂.

Bulk superconductivity confirmed by heat capacity jump.

Electronic structure shows mixed quasi-2D and 3D character.

Abstract

Superconductivity is observed with critical temperature $T_{c}$ = 2.0 K in self-flux-grown single crystals of $CaBi_{2}$. This material adopts the $ZrSi_{2}$ structure type with lattice parameters a = 4.696(1) $\AA$, b = 7.081(2) $\AA$ and c = 4.611(1) $\AA$. The crystals of $CaBi_{2}$ were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at $T_{c}$ is $\Delta C/\gamma T_{c}$ = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient $\gamma$ = 4.1 $mJ\: mol^{-1}\, K^{-2}$ and the Debye temperature $\Theta_{D}$ = 157 K. The electron-phonon coupling strength is $\lambda_{el-ph}$ = 0.59, and the thermodynamic critical field $H_{c}$ is low, between 111 and 124 Oe $CaBi_{2}$ 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\textendash 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.