Prediction of High-Temperature Superconductivity in Monolayer h-AlH₂ at Ambient Pressure

Although hydrides such as LaH10 are experimentally confirmed to possess high superconducting critical temperature (T-c) of 250-260 K under 170-200 GPa, it is still a tough challenge to be applied. It is highly anticipated to find hydride superconductors with relatively high T-c at low or ambient pressure. Reducing the dimensionality of materials can induce unexpected properties that are distinct from their bulk counterparts, and whether it can modulate the superconducting properties deserves further investigation. Herein, a new 2D monolayer aluminum hydride h-AlH(2 )is theoretically predicted under ambient pressure based on the first-principles calculations. Since the electronic structures of h-AlH(2)reveal the metallicity, the electron-phonon coupling (EPC) and possible phonon-mediated superconductivity are investigated. Based on the isotropic Eliashberg equation, the calculated EPC constant lambda of h-AlH2 is 1.16, and the T-c is up to 42.6 K. The EPC mainly originates from the coupling between electrons of Al-s,p(x),p(y), and H-s orbitals and the in-plane vibration modes of H atoms. Especially, the T-c can be enhanced to 63.7 K by applying 3% biaxial tensile strain. Thus, the predicted h-AlH(2 )provides a new platform for finding hydride superconductors in low-dimensional materials at ambient pressure.