Coexistence of superconductivity and superionicity in Li2MgH16

We study superconductivity in the superionic phase of the clathrate hydride Li₂MgH₁₆, 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 [λ(0)=3.7] and a high superconducting transition temperature (Tc) of 277 K under 260 GPa, at which the material is still superionic. Tc is significantly suppressed compared with the result Tc=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 Li₂MgH₁₆.