Multi-block element modulation enables high temperature superconductivity in quaternary hydrides at low pressures

Abstract

Hydrides synthesis guided by structural design has significantly advanced the exploration for high-temperature superconductors but most hydrides still require extremely high pressures, which hinders their practical applications. Here, we propose a design strategy based on alloyed A15 frameworks, guided by chemical bonding principles and the strategic tuning of elements from different blocks of the periodic table, through which a series of superconducting quaternary XYZ₂H₁₂ hydrides were constructed. First-principles calculations identified six thermodynamically stable hydrides out of 80 candidates at 20 GPa, with GaAlZr₂H₁₂ and GaAlHf₂H₁₂ exhibiting T_c of 74 K and 69 K, respectively. Notably, the T_c of GaAlZr₂H₁₂ increases to 79 K at 15 GPa, exceeding the temperature of liquid nitrogen. Importantly, we reveal that the incorporation of p- and d-block elements enhances the density of states at the Fermi level and induces phonon softening via Fermi surface nesting, thereby significantly enhancing electron-phonon coupling strength. And strong electron-phonon matrix elements, primarily driven by hydrogen vibrations, significantly contribute to boost superconductivity in GaAlZr₂H₁₂ and GaAlHf₂H₁₂. Our study demonstrates that the bonding-guided approach combined with multiblock elemental tuning strategy offers an effective route for designing stable hydride superconductors, while providing guidance for realizing high-T_c superconductor under experimentally accessible low pressures.