Superconductivity above 105 K in Nonclathrate Ternary Lanthanum Borohydride below Megabar Pressure

Hydrides are promising candidates for achieving room-temperature superconductivity, but a formidable challenge remains in reducing the stabilization pressure below a megabar. In this study, we successfully synthesized a ternary lanthanum borohydride by introducing the nonmetallic element B into the La-H system, forming robust B-H covalent bonds that lower the pressure required to stabilize the superconducting phase. Electrical transport measurements confirm the presence of superconductivity with a critical temperature (T_c) of up to 106 K at 90 GPa, as evidenced by zero resistance and T_c shift under an external magnetic field. X-ray diffraction and transport measurements identify the superconducting compound as LaB₂H₈, a nonclathrate hydride, whose crystal structure remains stable at pressures as low as ∼ half megabar (59 GPa). Stabilizing superconductive stoichiometric LaB₂H₈ in a submegabar pressure regime marks a substantial advancement in the quest for high-T_c superconductivity in polynary hydrides, bringing us closer to the ambient pressure conditions.