The hunt for high temperature superconductivity has been reinvigorated by the experimental discovery that compressed H2S exhibits a Tc of up to 203K at megabar pressures (1Mbar=100GPa). A collaboration between the University of Cambridge and Jilin University has published the results of a computational search for materials that might superconduct at even higher temperatures.
An extensive search for the stable structures and compositions of rare earth hydrides was performed using first principles density functional theory based methods. The superconducting transition temperatures for the stable metallic compounds were calculated using the same theoretical techniques that were used to anticipate the superconductivity in dense hydrogen sulphide. The highest temperatures were predicted for pressures that are around those found in the center of the Earth. It is a challenge for the future to find materials that superconduct at high temperatures and everyday low pressures.
Room-temperature superconductivity has been a long-held dream and an area of intensive research. Recent experimental findings of superconductivity at 200 K in highly compressed hydrogen (H) sulfides have demonstrated the potential for achieving room-temperature superconductivity in compressed H-rich materials. We report first-principles structure searches for stable H-rich clathrate structures in rare earth hydrides at high pressures. The peculiarity of these structures lies in the emergence of unusual H cages with stoichiometries H24, H29, and H32, in which H atoms are weakly covalently bonded to one another, with rare earth atoms occupying the centers of the cages. We have found that high-temperature superconductivity is closely associated with H clathrate structures, with large H-derived electronic densities of states at the Fermi level and strong electron-phonon coupling related to the stretching and rocking motions of H atoms within the cages. Strikingly, a yttrium (Y) H32 clathrate structure of stoichiometry YH10 is predicted to be a potential room-temperature superconductor with an estimated Tc of up to 303 K at 400 GPa, as derived by direct solution of the Eliashberg equation.