Superconductivity in sodalite-like yttrium hydride clathrates

Abstract

Motivated by the discovery of near-room-temperature superconductivity in the sodalite-like clathrate hydride ${\mathrm{LaH}}_{10}$, we report ab initio calculations of the superconducting properties of two closely related hydrides ${\mathrm{YH}}_{6}$ and ${\mathrm{YH}}_{10}$ for which an even higher ${T}_{\mathrm{c}}$ has been predicted. Using fully anisotropic Migdal-Eliashberg theory with Coulomb corrections, we find almost isotropic superconducting gaps, resulting from a uniform distribution of the coupling over states of both Y and H sublattices. The Coulomb screening is rather weak, resulting in a Morel-Anderson pseudopotential ${\ensuremath{\mu}}^{*}=0.11$, at odds with claims of unusually large ${\ensuremath{\mu}}^{*}$ in lanthanum hydrides. The corresponding critical temperatures at 300 GPa exceed room temperature (${T}_{\mathrm{c}}=290$ and 310 K for ${\mathrm{YH}}_{6}$ and ${\mathrm{YH}}_{10}$), in agreement with a previous isotropic-gap calculation. We estimate anharmonic effects to be weak. The different response of these two compounds to external pressure along with a comparison to low-${T}_{\mathrm{c}}$ superconducting ${\mathrm{YH}}_{3}$ may inspire strategies to improve the superconducting properties of this class of hydrides.