Research Progress on High-Temperature H2-Molecular-Type Hydride under High Pressure

The synthesis of the room-temperature superconductor LaSc₂H₂₄ represents a significant milestone in the field of superconductivity research. A central goal of subsequent studies is to lower the stabilization pressure required for hydrogen-rich superconductors, thereby establishing a theoretical foundation and technical pathway toward achieving low-pressure room-temperature superconductivity. This paper reviews recent advances in the prediction and experimental synthesis of hydride materials, with a particular focus on a promising strategy for realizing high-temperature superconductivity at reduced pressures — namely, molecular hydrogen-based hydrides. The superconducting mechanism dominated by molecular H₂ units is redefined, offering a new perspective for understanding phonon-mediated superconductivity. In molecular hydrogen-based hydrides, a nearly free-electron gas behavior has been clearly observed. These delocalized electrons exhibit metallic bonding characteristics while retaining fragments of molecular hydrogen. This finding indicates that the essential condition for superconducting transition is the formation of a Fermi sea hosting Cooper pairs, rather than complete dissociation into atomic hydrogen. The generation mechanism of the free-electron gas in these materials can be effectively explained using a finite potential well model. The distinctive electronic properties of these compounds under high pressure, combined with enhanced electron-phonon coupling, establish a novel paradigm for designing low-pressure, high-temperature, and potentially room-temperature superconductors.