Superconducting phase diagram of H₃S under high magnetic fields

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH₁₀ re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fields μ₀H_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 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 H₃S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.