MgPd2Sb : A Mg-based Heusler-type superconductor

We report the synthesis and physical properties of a full Heusler compound, $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$, which we found to show superconductivity below ${T}_{c}=2.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$ was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure [$Fm\text{\ensuremath{-}}3m, a=6.4523(1)\phantom{\rule{0.16em}{0ex}}\AA{}$] were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$ is a type-II, weak coupling superconductor (${\ensuremath{\lambda}}_{e\text{\ensuremath{-}}p}=0.53$). The observed pressure dependence of ${T}_{c}$ ($\mathrm{\ensuremath{\Delta}}{T}_{c}/p\ensuremath{\approx}--0.23\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{GPa}$) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$ were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters to those of all reported Heusler-type superconductors.