Superconductivity in Layered M B ₂ C ₄ (M = Pb, Sc, Tc, Re, and Fe)

Stimulated by recently reported high-critical-temperature ( T c ) intercalated layered M B 3 C 3 (M = Mg, Ca, Sr, Sc, Y, and Ti) and X B 2 C 2 (X = Li, Na, K, Ca, Sr, La and Cu), where σ bands provide superconducting carriers (paired electrons), we investigate a new class of M B 2 C 4 (M = Pb, Sc, Tc, Re, and Fe) systems based on first-principles calculations. In these compounds, B and C atoms form sp 2 -hybridized honeycomb layers, with M atoms acting as electron donors in the interlayers. Our calculations suggest that all M B 2 C 4 are excellent metallic conductors. Importantly, except for FeB 2 C 4, all compounds are phonon-mediated superconductors at ambient pressure, with T c ranging from 0.6 to 3.3 K. Remarkably, ReB 2 C 4 exhibits the highest T c of 3.3 K, owing to the large electronic density of states (eDOS) dominated by d electrons near the Fermi level (FL). Intriguingly, the magnetism of FeB 2 C 4 is induced by d electrons, which may act as a suppressing factor rather than the definitive reason for the absence of superconductivity (SC).