Superconductivity in 122-type antimonide BaPt${}_2$Sb${}_2$

The crystal structure, superconducting properties, and electronic structure of a novel superconducting 122-type antimonide, BaPt${}_2$Sb${}_2$, have been investigated by measurements of powder X-ray diffraction patterns, electrical resistivity, ac magnetic susceptibility, specific heat as well as ab-initio calculations. This material crystallizes in a new-type of monoclinic variant of the CaBe${}_2$Ge${}_2$-type structure, in which Pt${}_2$Sb${}_2$ layers consisting of PtSb${}_4$ tetrahedra and Sb${}_2$Pt${}_2$ layers consisting of SbPt${}_4$ tetrahedra are stacked alternatively and Ba atoms are located between the layers. Measurements of electrical resistivity, ac magnetic susceptibility and specific heat revealed that BaPt${}_2$Sb${}_2$ is a superconducting material with a $T_{\rm c}$of1.8K\mathrm{.}Theelectronicheatcapacitycoefficient$\gamma_{\rm n}$ and Debye temperature ${\theta }_{\mathrm{D}}$ were 8.6(2) mJ/mol K${}^2$ and 146(4) K, where the figures in parentheses represent the standard deviation. The upper critical field ${\mu }_0{H}_{\mathrm{c}2}(0)$ and the Ginzburg-Landau coherent length $\xi (0)$ were determined to be 0.27 T and 35 nm. Calculations showed that it has two three-dimensional Fermi surfaces (FSs) and two two-dimensional FSs, leading to anisotropic transport properties. The d-states of the Pt atoms in the Pt2Sb2 layers mainly contribute to $N(E_{\mathrm{F}})$. A comparison between experimental and calculated results indicates that BaPt${}_2$Sb${}_2$ is a superconducting material with moderate coupling.