Al-Based Few-Hydrogen Metal-Bonded Perovskite High-$T_c$ Superconductor Al${}_4$H up to 54 K under Atmospheric Pressure

Multi-hydrogen lanthanum hydrides have shown the highest critical temperature $T_c$ at 250-260 K under 170-200 GPa. However, such high pressure is a great challenge for sample preparation and practical application. To address this challenge, we propose a novel design strategy for ambient-pressure high-$T_c$ superconductors by constructing new few-hydrogen metal-bonded perovskite hydrides, such as Al-based superconductor $\mathrm{A}{\mathrm{l}}_4\mathrm{H}$, with better ductility than the well-known multi-hydrogen, cuprate and Fe-based superconductors. Based on the Migdal-Eliashberg theory, we predict that the structurally stable $\mathrm{A}{\mathrm{l}}_4\mathrm{H}$ has a favorable high $T_c$ up to 54 K under atmospheric pressure, similar to SmOFeAs.