Superconducting properties of rare-earth boron hydrides at high pressure studied by first-principles calculations

It is a long-thought proposal that dense light-element molecular hydrides, such as diborane ($B_2{H}_6$) and methane (${\mathrm{CH}}_4$), offer an ideal platform to search for phonon-mediated superconductors. However, these hydrides are often unstable under sufficiently high pressure, e.g., $B_2{H}_6$ decomposed into BH and $H_2$ at pressures of above 153 GPa, which are unlikely to exhibit high superconductivity. Here, we find a feasible route to stabilize these light-element molecular hydrides with high superconductivity under high pressure by high-throughput structure searches and first-principles calculations. We uncover a series of stable H-rich rare-earth ($R$) metal based boron hydrides $R{B}_2{H}_{10}$ with polydiborane networks. Strikingly, ${\mathrm{YB}}_2{H}_{10}$ is predicted to be a high-temperature superconductor with unprecedentedly critical temperature ( $T_c$ ) of up to 93 K under 150 GPa. The present findings open a route to stabilize the unstable diborane by bringing the additional $R$ metals into the lattice under high pressure, as well as tuning the superconductivity among diborane-based hydrides and other similar dense light-element molecular hydrides.