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 T-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 mu* = 0.11, at odds with claims of unusually large mu* in lanthanum hydrides. The corresponding critical temperatures at 300 GPa exceed room temperature (T-c = 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-T-c superconducting YH3 may inspire strategies to improve the superconducting properties of this class of hydrides.