High-temperature superconductivity on the verge of a structural instability in lanthanum superhydride

A possibility of high, room-temperature superconductivity was predicted for metallic hydrogen in the 1960s. However, metallization and superconductivity of hydrogen are yet to be unambiguously demonstrated in the laboratory and may require pressures as high as 5 million atmospheres. Rare earth based "superhydrides" such as LaH10 can be considered a close approximation of metallic hydrogen even though they form at moderately lower pressures. In superhydrides the predominance of H-H metallic bonds and high superconducting transition temperatures bear the hallmarks of metallic hydrogen. Still, experimental studies revealing the key factors controlling their superconductivity are scarce. Here, we report on the pressure and magnetic field response of the superconducting order observed in LaH10. For LaH10 we find a correlation between superconductivity and a structural instability, strongly affecting the lattice vibrations responsible for the superconductivity.