Unlocking the origin of stability and superconductivity in LaBeH8 at submegabar pressure

The recent synthesis of LaBeH₈ with a superconducting critical temperature (Tc) up to 110 K at a pressure of 80 GPa generates great hope to achieve high-temperature superconductivity in ternary hydrides at submegabar pressure. However, the underlying mechanism governing its unexpected stability and high-temperature superconductivity remains elusive, which impedes the demanding design of other high-Tc ternary hydrides on the way to room-temperature superconductivity. Here, we conducted a comprehensively theoretical study to reveal the origin of the stability and superconductivity of LaBeH₈. We found that LaBeH₈ could be viewed as a rocksalt compound of La²⁺[BeH₈]^2- and its unexpected stability lies in the emergence of an unusually negatively charged molecular [BeH₈]^2- unit containing polarized Be-H covalent bonds. This [BeH₈]^2-unit gives rise to an intrinsic metallic feature in the solid, and its interaction with neighboring ones via weak H-H coupling contributes mostly to the high-temperature superconductivity. Our current results offer a key perspective of high-temperature superconductivity among ternary hydrides, thus inspiring a potential developing strategy to design high-Tc hydrides via the exploration of similar intrinsic metallic salt structure motifs containing a variety of hydrogen-rich covalent units.