Recent high-throughput searches for conventional superconductors suggest that the superconducting transition temperature is inversely correlated with thermodynamic stability, making the discovery of high-temperature conventional superconductors at ambient pressure unlikely. However, metastable compounds may provide a viable pathway toward higher transition temperatures.

Motivated by our previous study of metastable RbPH3, we systematically explore ABH3 compounds at ambient pressure, where A is an alkali metal and B is a pnictogen element. Similar to the case of RbPH3, we find that four compounds are metastable at ambient pressure due to quantum anharmonic effects. Crystal structure prediction reveals that three of these compounds lie within 50 meV/atom above the convex hull at 25 GPa, suggesting that their synthesis may be achievable at relatively low pressures and indicating possible synthesis pathways. The strong quantum anharmonic effects are evidenced through strong renormalization of hydrogen dominated phonon bands. Due to the significant contribution of hydrogen-derived electronic states at the Fermi level, all proposed compounds are metallic and exhibit superconductivity above liquid nitrogen temperatures.