Stabilizing Phonon-Mediated High-Temperature Superconductivity via Helium Substitution in Pressurized Lithium Hexahydride

Exploring thermodynamics and superconductivity is crucial, particularly in the context of their captivating nature within high-pressure physics. This study focuses on characterizing the thermodynamics and superconductivity of the metallic phase of lithium hexahydride, stabilized through helium substitution, a phenomenon noteworthy for its substantial reduction in the required pressure. Employing a first-principles evolutionary algorithm based on density functional theory, our predictions highlight that LiHeH6 is the most stable structure. Remarkably, our observations indicate that this reduction significantly influences the emergence of high-temperature superconductivity in the LiHeH6 phase, elevating the critical temperature (Tc) of superconductivity by approximately 177 K at 90 GPa. The phenomenon is comprehensively elucidated by the Allen-Dynes modified McMillan formalism, wherein the enhanced Tc is predominantly influenced by the strength of the electron-phonon coupling constant. Additionally, an examination of the superconducting gap, employing the anisotropic Migdal-Eliashberg formalism, reveals a noteworthy disparity in Tc values compared to the Allen-Dynes modified McMillan formalism as pressure increases. Theoretical analysis of superconductivity in LiHeH6 highlights the significant impact of the Eliashberg function, particularly attributed to medium- and low-frequency phonon modes originating from helium atoms. The Allen-Dynes modified McMillan results effectively describe the superconducting state, especially in materials with a conventional bulk metallic structure. This research bears significance for the field of materials science, especially for those involved in the study of high-pressure superconductors. These findings underscore the crucial role of helium in influencing thermodynamics and lattice dynamics, shedding light on the way a substantial reduction in required pressure enhances the superconductivity of metal hydrides.