Superconducting phase diagram of HS under high magnetic fields.

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fields μH(T) of superconducting HS under a record-high combination of applied pressures up to 160 GPa and fields up to 65 T. We find that H(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 of H(T) to the WHH formalism yields negligible values for the Maki parameter α and the spin-orbit scattering constant λ. However, H(T) is well-described by a model based on strong coupling superconductivity with a coupling constant λ ~ 2. We conclude that HS behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.