The discovery of near room temperature superconductivity in clathrate hydrides has ignited the search for both higher temperature superconductors and deeper understanding of the underlying physical phenomena. In a conventional electron-phonon mediated picture for the superconductivity for these materials, the high critical temperatures predicted and observed can be ascribed to the low mass of the protons, but this also poses nontrivial questions associated with how the proton dynamics affect the superconductivity. Using clathrate superhydrideLi2MgH16as an example, we show throughab initiopath integral simulations that proton diffusion in this system is remarkably high, with a diffusion coefficient, for example, reaching6×10−6 cm2/sat 300 K and 250 GPa. The diffusion is achieved primarily through proton transfer among interstitial voids within the otherwise rigidLi2Mgsublattice at these conditions. The findings indicate the coexistence of proton quantum diffusion together with hydrogen-induced superconductivity, with implications for other very-high-temperature superconducting hydrides.
(e) The  view of Li2MgH16. (f),(g) Proton density distributions at∼30 K and 250–300 GPa calculated from PIMD with 16 beads in the cubic cell of 152 atoms; selected protons are marked by different colors.
Hui Wang works at Key Laboratory for Photonic and Electronic Bandgap Materials (Ministry of Education), School of Physics and Electronic Engineering, Harbin Normal University. Yansun Yao works at Department of Physics and Engineering Physics, University of Saskatchewan, Canada. Feng Peng works at College of Physics and Electronic Information, Luoyang Normal University. Hanyu Liu works at International Center for Computational Method, Software, State Key Laboratory of Superhard Materials, and Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University. Russell Hemley works at Departments of Physics and Chemistry, University of Illinois at Chicago, USA. Hui Wang and Yansun Yao contributed equally to this work. Hui Wang and Hanyu Liu are corresponding authors.
This work was supported by the National Natural Science Foundation of China, the Program for JLUSTIRT, and the computing facilities at the High Performance Computing Centre of Jilin University and Beijing Super Cloud Computing Center.