Superconductivity of abnormal magic-stoichiometric Na3Cl and Li3Cl salt crystals at normal pressure

The identification of new materials with superconducting properties is the pursuit in the realm of superconductivity research. Here, we excitingly show that the simplest salt used daily can be made a superconductor at normal pressure only by adjusting its stoichiometry of Na, Li, and Cl as Na3Cl or Li3Cl at normal pressure based on first-principles calculations. These abnormal Na-Cl stoichiometric crystal of 3:1, the first "magic" ratio, include metallic atoms (Na, Li) in the core as well as hybridization of ionic and metallic bonding, facilitating the electron-phonon coupling for superconductivity with a critical temperature Tc of 0.13 and 1.17 K. The flat bands and van Hove singularities near the Fermi level produce large densities of states, which is beneficial for the emergence of superconductivity. The crystal with abnormal Na (Li)-Cl magic stoichiometry is a precisely tunable, purely sodium (lithium) and chloride-based, which is, therefore, an ideal material for designing and understanding abnormal stoichiometric crystals. The methodology of constructing this abnormal crystal may be general to almost all elements, which could lead to insights into the physics of other conventional superconductors and even high-critical-temperature superconductors.