Room-Temperature Superconductivity in Metallic Alloy S_0.5He_0.5H₃ under High Pressures

We investigate the effect of He substitution in the superconducting phase of H3S using a structural stability–driven evolutionary algorithm based on density functional theory (DFT). Our findings reveal that the composition S0.5He0.5H3 results in a thermodynamically stable structure. The resulting S0.5He0.5H3 compound adopts a simple cubic structure with the space group Pm3̅ under high-pressure conditions. Regarding the superconducting properties of Pm3̅ S0.5He0.5H3, we demonstrate that the Eliashberg spectral function is strongly linked to the electron–phonon coupling parameter’s occurrence of strong coupling. We further elucidate the superconducting parameters by utilizing the bandwidth function, which offers a simplified analytical depiction of the Eliashberg spectral function. Using first-principles calculations based on DFT combined with the Migdal–Eliashberg formalism, the structure demonstrates isotropic superconductivity with a high critical temperature (Tc) exceeding room temperature, reaching 329 K at a pressure of 350 GPa. These findings highlight the potential of substitution in H3S, significantly broadening and diversifying the structural landscape for exploring and predicting high-temperature superconductivity, particularly with enhancements induced by helium at high pressures.