Coexistence of superconductivity and superionicity in Li2MgH16

We study superconductivity in the superionic phase of the clathrate hydride ${\mathrm{Li}}_{2}{\mathrm{MgH}}_{16}$, where hydrogen ions diffuse among the lattice formed by lithium and magnesium ions. By employing the stochastic path-integral approach, we nonperturbatively take into account the effects of quantum diffusion and anharmonic vibrations. Our calculations reveal strong electron-ion coupling $[\ensuremath{\lambda}(0)=3.7]$ and a high superconducting transition temperature $({T}_{c})$ of 277 K under 260 GPa, at which the material is still superionic. ${T}_{c}$ is significantly suppressed compared with the result ${T}_{c}=473$ K obtained from the conventional approach based on the harmonic approximation. Our study, based on a first-principles approach applicable to superionic systems, indicates that the superconductivity and superionicity can coexist in ${\mathrm{Li}}_{2}{\mathrm{MgH}}_{16}$.