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The 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 and may require pressures as high as 5 million atmospheres. Rare earth based “superhydrides”, such as LaH₁₀, can be considered as 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 the pressure and magnetic field dependence of the superconducting order observed in LaH₁₀. We determine that the high-symmetry high-temperature superconductingFm-3mphase of LaH₁₀can be stabilized at substantially lower pressures than previously thought. We find a remarkable correlation between superconductivity and a structural instability indicating that lattice vibrations, responsible for the monoclinic structural distortions in LaH₁₀, strongly affect the superconducting coupling.

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH₁₀re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fieldsμ₀H_c2(T) of superconducting H₃S under a record-high combination of applied pressures up to 160 GPa and fields up to 65 T. We find thatH_c2(T) displays a linear dependence on temperature over an extended range as found in multigap or in strongly-coupled superconductors, thus deviating from conventional Werthamer, Helfand, and Hohenberg (WHH) formalism. The best fit ofH_c2(T) to the WHH formalism yields negligible values for the Maki parameterαand the spin–orbit scattering constantλ_SO. However,H_c2(T) is well-described by a model based on strong coupling superconductivity with a coupling constantλ~ 2. We conclude that H₃S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.