LaBH$_{8}$: the first high-T$_{c}$ low-pressure superhydride

Abstract: In the last five years a large number of new high-temperature superconductors have been predicted and experimentally discovered among hydrogen-rich crystals, at pressures which are way too high to meet any practical application. In this work, we report the computational prediction of a hydride superconductor, LaBH${8}$, with a T${c}$ of 126 K at a pressure of 50 GPa, thermodynamically stable above 100 GPa, and dynamically stable down to 40 GPa, an unprecedentedly low pressure for high-T${c}$ hydrides. LaBH${8}$ can be seen as a ternary sodalite-like hydride, in which a metallic hydrogen sublattice is stabilized by the chemical pressure exerted by the guest elements. The combination of two elements with different atomic sizes in LaBH$_{8}$ realizes a more efficient packing of atoms than in binary sodalite hydrides. A suitable choice of elements may be exploited to further reduce the stabilization pressure to ambient conditions.