Coexistence of Superionicity and Superconductivity in Li₂MgH₁₆

Recently, we and collaborators develop a stochastic path-integral approach (SPIA) to study ion-mediated superconductivity in general systems. The method makes no assumptions of the nature of ion motion, and thus allows studies beyond harmonic solids. We implement the method based on density-functional theory (DFT). Applications predict superconducting liquid hydrogen and verify the strong effect of anharmonicity in hydride sulfide.

In this work, 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 SPIA, we non-perturbatively take into account the effects of quantum diffusion and anharmonic vibrations. Our calculations show strong electron-ion coupling (λ(0)) 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, predicts that the superconductivity and superionicity can coexist in Li₂MgH₁₆.