Near-room-temperature superconductivity of Mg/Ca substituted metal hexahydride under pressure

Abstract

A quest for room-temperature superconductors is undergoing rapid innovation due to the continuing proliferation of experimental and theoretical researches on high-pressure physics. Hydrogen-caged metal compounds have been proposed to promote high critical temperature superconductivity at pressures, providing a decent opportunity to investigate related phenomena at experimentally attainable pressures. This breakthrough is attributable to the uplifting key parameters, such as electron-phonon interaction and maximum phonon frequency, once thought to be limited, by utilising high pressures. A large class of metal polyhydrides has been theoretically proposed and experimentally realised to promote near-room-temperature superconductivity under high pressures. In this work, we theoretically reported the near-room-temperature superconductivity in a symmetrically Mg/Ca substituted hexahydride, i.e. Mg0.5Ca0.5H6. We showed that this ternary Mg0.5Ca0.5H6 compound adopts an Im3¯m structure, wherein a metal atom is embedded in a H24 cage, is thermodynamically and dynamically stable at pressures ranging from 200 to 400 GPa. The analyses of the electronic band structure, Fermi surface topologies, phonon dispersion, and spectral function manifest strong support for superconductivity. We obtained λ=2.53 and ωlog=1,400K for our Mg/Ca substituted hexahydride at 200 GPa, exhibiting a near-room-temperature Tc of 288 K, which completely exceeds the calculated Tc of its parent compounds, i.e. MgH6 and CaH6.