Superconductivity in sodalite-like yttrium hydride clathrates

Motivated by the discovery of near-room-temperature superconductivity in the sodalite-like clathrate hydride LaH10, we report ab initio calculations of the superconducting properties of two closely related hydrides YH6 and YH10, for which an even higher Tc 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 μ∗=0.11, at odds with claims of unusually large μ∗ in lanthanum hydrides. The corresponding critical temperatures at 300 GPa exceed room temperature (Tc= 290 and 310 K for YH6 and YH10), 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-Tc superconducting YH3 may inspire strategies to improve the superconducting properties of this class of hydrides.