Two-Dimensional Rare-Earth Metal Phosphides: From Weyl Semimetal to Semiconductor

Two-dimensional (2D) nanomaterials have garnered extensive attention owing to their unique properties and versatile application. Here, a family of 2D rare-earth metal phosphides (M₂P, M = Sc, Y, La) and their derivatives M₂POT (T = F, OH) is developed to find their topological and electronic properties on the basis of density functional theory simulations. We show that the 2D M₂P compounds are most possibly obtained from thermodynamically stable M₂InP by chemical exfoliation. The In with a substantial atomic radius of 156 pm exhibits weak polarization ability, resulting in homogeneity of the electron cloud and a weakening of the M-In bond relative to the M-P bond. Upon exfoliation of the In layer, the M₂²⁺P^3-:e^- emerges as an electride with surface electrons, which is attributed to the larger ion radius and lower electronegativity of M²⁺ ions in M₂P. The metallic M₂P is found to be a Weyl semimetal derived from the contribution of surface electrons. Further, by leveraging the high reactivity of surface electrons, surface functionalization can produce M₂POT compounds with the increased valence state of M³⁺, which results in their semiconducting properties characterized by high carrier mobilities and strong built-in electronic fields. These distinct topological and electronic characteristics position the 2D M₂P and M₂POT as promising candidates for a wide range of applications.