Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH$_{ 10}$ under megabar pressures. This SC of compressed LaH$_{ 10}$ has been explained in terms of strong electron-phonon coupling (EPC), but the mechanism of how the large EPC constant and high superconducting transition temperature $T_{ \rm c}$ are attained has not yet been clearly identified. Based on the density-functional theory and the Migdal-Eliashberg formalism, we reveal the presence of two nodeless, anisotropic superconducting gaps on the Fermi surface (FS). Here, the small gap is mostly associated with the hybridized states of H $s$ and La $f$ orbitals on the three outer FS sheets, while the large gap arises mainly from the hybridized state of neighboring H $s$ or $p$ orbitals on the one inner FS sheet. Further, we find that the EPC constant of compressed YH$_{ 10}$ with the same sodalite-like clathrate structure is enhanced due to the two additional FS sheets, leading to a higher $T_{ \rm c}$ than LaH$_{ 10}$. It is thus demonstrated that the multiband pairing of hybridized electronic states is responsible for the large EPC constant and room-temperature SC in compressed hydrides LaH$_{ 10}$ and YH$_{ 10}$.
Categories: cond-mat.supr-con cond-mat.mtrl-sci