Superconducting phase diagram of H 3 S under high magnetic fields.

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH ₁₀ re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fields μ ₀ H _c2 (T) of superconducting H ₃ S under a record-high combination of applied pressures up to 160 GPa and fields up to 65 T. We find that H _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 of H _c2 (T) to the WHH formalism yields negligible values for the Maki parameter α and the spin-orbit scattering constant λ _SO . However, H _c2 (T) is well-described by a model based on strong coupling superconductivity with a coupling constant λ ~ 2. We conclude that H ₃ S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.