Superconductivity of LaH 10 and LaH 16 polyhydrides

Recent experiments have established previously predicted ${\mathrm{LaH}}_{10}$ as the highest-temperature superconductor, with ${T}_{C}$ up to 250--260 K [Drozdov et al., Nature (London) 569, 528 (2019); Somayazulu et al., Phys. Rev. Lett. 122, 027001 (2019)]. In this work we explore the high-pressure phase stability and superconductivity of lanthanum hydrides ${\mathrm{LaH}}_{m}$. We predict the stability of the hitherto unreported polyhydride $P6/mmm\ensuremath{-}{\mathrm{LaH}}_{16}$ at pressures above 150 GPa; at 200 GPa, its predicted superconducting ${T}_{C}$ is 156 K, the critical field ${\ensuremath{\mu}}_{0}{H}_{C}(0)$ is approximately 35 T, and the superconducting gap is up to 35 meV. We revisit the superconductivity of ${\mathrm{LaH}}_{10}$ and find its ${T}_{C}$ to be up to 259 K at 170 GPa from solving the Eliashberg equation and 271 K from solving the gap equation within the superconducting density functional theory, which also allows us to compute the Coulomb pseudopotential ${\ensuremath{\mu}}^{*}$ for ${\mathrm{LaH}}_{10}$ and ${\mathrm{LaH}}_{16}$.