A central question in superconductivity is how a semimetal such as antimony, normally nonsuperconducting, can host a robust superconducting state upon Au incorporation. We investigate this problem in metastable ${\mathrm{Sb}}_{0.83}{\mathrm{Au}}_{0.17}$, which crystallizes in the simple cubic $\alpha \text{−}\mathrm{Po}$-type structure stabilized through high-pressure and high-temperature synthesis. Bulk measurements of magnetic susceptibility, resistivity, and heat capacity establish type-II superconductivity with $T_c\approx 8\mathrm{K}$. The superconducting state exhibits strong electron-phonon coupling (${\lambda }_{\mathrm{ep}}=0.91$) and the single-gap $s$-wave model yields a superconducting gap of $\mathrm{\Delta }=$ 2.02 $k_B{T}_c$, exceeding the BCS weak-coupling limit. Heat-capacity data reveal low-energy Einstein modes and a pronounced Boson peak in the $\frac{C_{\mathrm{phonon}}}{T^3}$ vs $T$ plot, highlighting phonon softening as a key factor in the enhanced coupling. We argue that the emergence of superconductivity is driven by the cooperative effect of soft phonons and strong electron-phonon interactions. Density-functional theory calculations indicate a finite density of states at the Fermi level, consistent with a metallic behavior in contrast to the semimetallic nature of pristine Sb.

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• Electron-phonon coupling
• Magnetic susceptibility
• Pressure effects
• Superconductivity
• Type-II superconductors
• Density functional theory
• Resistivity measurements
• Specific heat measurements
• X-ray diffraction