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.