High-pressure synthesis of superconducting clathratelike YH4

Abstract

Pursuing room-temperature superconductors has been a major theme in physics and material sciences since the discovery of superconductivity in 1911. In light of the tremendous progress that has been made in hydrogen-based superconductors with record ${T}_{c}\ensuremath{\sim}260\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in binary fcc $\mathrm{La}{\mathrm{H}}_{10}$, it is natural to explore more similar phases in hydrogen-rich materials. Y and La are conventionally grouped together with the lanthanide elements due to the similarities in their outer electron configurations and properties. The yttrium-hydrogen system is the most attractive candidate with high ${T}_{c}$ among all binary metal-hydrogen systems theoretically studied so far. Here we report the synthesis of the $I4/mmm\text{\ensuremath{-}}\mathrm{Y}{\mathrm{H}}_{4}$ phase and determine its superconducting transition with maximum ${T}_{c}\ensuremath{\sim}88\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 155 GPa. The decrease in critical temperature under an external magnetic field suggests the upper critical magnetic field of about 14--22 T at megabar pressures consistent with theoretical data. By making the overlapping analysis, we elucidate that the stabilization of clathrate structures through Y atoms and the high-frequency hydrogen sublattice vibrations contribute effectively to strong electron-phonon coupling and therefore high-temperature superconductivity in the $I4/mmm\text{\ensuremath{-}}\mathrm{Y}{\mathrm{H}}_{4}$ and $Im\overline{3}m\text{\ensuremath{-}}\mathrm{Y}{\mathrm{H}}_{6}$ phases.