Phonon-mediated superconductivity in metastable phases of scandium–helium compounds under high pressure

Scandium–helium compounds have been predicted as viable phases under high pressure through ab initio random structure searching based on density functional theory. In this work, structural predictions provide crucial insights into their crystal frameworks, which exhibit delocalized bonding characteristics with neighboring atoms. The ScHe, ScHe2, and ScHe3 phases are identified as metastable yet capable of stabilizing metallic states. Their superconducting properties are further examined using the Allen–Dynes modified McMillan (ADM) equation and the original McMillan (McM) formalism. The role of electron–phonon coupling (EPC) is emphasized, as moderate EPC strength contributes to the evolution of the critical temperature (Tc) superconductivity. The results reveal that ScHe, ScHe2, and ScHe3 all exhibit superconducting behavior, with predicted Tc values of 24 K for ScHe at 200 GPa, 53 K for ScHe2 at 300 GPa, and 33 K for ScHe3 at 200 GPa. Notably, ScHe2 exhibits a Tc of 92 K, as predicted by McMillan’s formalism, which is the highest among the Sc–He compounds considered in this work.