Pressure-stabilized graphenelike P layer in superconducting LaP2

MgB2-type superconductors are of great interest in chemistry and condensed matter physics due to their superconductivity dominated by the structural unit of graphene-like B. However, this kind of material is absent in phosphides resulting from the inherent lone pair electrons of phosphorus. Here, we report that a pressure-stabilized LaP2, isostructural to MgB2, shows superconductivity with a predicted Tc of 22.2 K, which is the highest among those of already known transition metal phosphides. Besides the electron-phonon coupling of graphene-like P, alike the role of the B layer in MgB2, La 5d/4f electrons are also responsible for the superconducting transition. The distinct P atomic arrangement is attributed to its sp2 hybridization and out-of-plane symmetric distribution of lone pair electrons. On the other hand, its dynamically stabilized pressure reaches as low as 7 GPa, a desirable feature of pressure-induced superconductors. Although P is isoelectronic to N and As, we hereby find the different stable stoichiometries, structures, and electronic properties of La phosphides compared with La nitrides/arsenides at high pressures.