Interplay of Superconductivity, Ferromagnetism, and Half-Metallicity in Gated Single-Layer g-C3N4

Graphitic carbon nitride (g-C3N4) hosts lone pairs arising from broken carbon–nitrogen bonds in its heptazine structure. These strongly localized and weakly hybridized states form ultraflat bands, potentially leading to correlated states when doped. Using first-principles calculations, we show that field-effect hole doping in single-layer g-C3N4 depletes these lone pairs, unveiling a rich phase diagram with a complex interplay of superconducting, half-metallic, and insulating ferromagnetic phases, even at very low charging and in the absence of transition metal ions. Our work highlights gated two-dimensional systems hosting lone pairs as a novel platform for strongly correlated states.