In-silico synthesis of lowest-pressure high-$T_{\text{c}}$ ternary superhydrides

Abstract

We report the theoretical prediction of two high-performing hydride superconductors BaSiH${}_8$ and SrSiH${}_8$. They are thermodynamically stable above pressures of $130$ and $174\text{GPa}$, respectively, and metastable below that. Employing anharmonic phonon calculations, we determine the minimum pressures of dynamical stability to be around $3\text{GPa}$ for BaSiH${}_8$ and $27\text{GPa}$ for SrSiH${}_8$, and using the fully anisotropic Migdal-Eliashberg theory, we predict $T_{\text{c}}$'s around $71$ and $126\text{K}$, respectively. We also introduce a method to estimate the lowest pressure of synthesis, based on the calculation of the enthalpy barriers protecting the BaSiH${}_8$ $Fm\bar{3}m$ structure from decomposition at various pressures. This $kinetic$ pressure threshold is sensibly higher than the one based on $dynamic$ stability, but gives a much more rigorous limit for synthesizability.

9 pages, 6 figures. Revised manuscript with minor changes. Supplemental Material available on the journal website (open access)

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