Coexistence of Zero-Dimensional Electride State and Superconductivity in AlH₂ Monolayer

Electrides, which confine “excess anionic electrons” in subnanometer-sized cavities of a lattice, are exotic ionic crystals. We propose a non-stoichiometric strategy to realize intrinsic two-dimensional (2D) superconducting electride. AlH₂ monolayer, which is structurally identical to 1H-MoS₂, possesses zero-dimensionally confined anionic electrons in the interstitial sites of Al triangles, corresponding to a chemical formula of AlH₂⁺e⁻. The interaction between interstitial anionic electrons (IAEs) and host cation lattice mainly accounts for stabilization of 1H-AlH₂ electride. Impressively, 1H-AlH₂ monolayer is an intrinsic Bardeen–Cooper–Schrieffer superconductor with T_c = 38 K, which is the direct consequence of strong coupling of the H-dominated high electronic states with Al acoustic branch vibrations and mid-frequency H-derived phonon softening modes caused by Kohn anomalies. Under tensile strain, IAEs transform into itinerant electrons, favoring the formation of stable Cooper pairs. Therefore, T_c reaches up to 53 K at a biaxial fracture strain of 5%. Our findings provide valuable insights into the correlation between non-stoichiometric electrides and superconducting microscopic mechanisms at the 2D limit.