Tuning the Crystalline Structure, Bandgap, and Topological Properties of 2D Fullerites via Heavy Element Doping

Well-designed two-dimensional (2D) honeycomb lattices offer a tunable platform for studying massless Dirac quasiparticles and their topological and correlated phases. The fullerene (C_n) molecules and fullerites have attracted enormous attention, whereas their 2D counterparts are rarely studied. Using first-principles calculations, we demonstrate that the C_n (n>20) fullerenes prefer the close-packing arrangement, while the heavy-element (Sb, Te, Pb, and Bi) doped C₂₈ fullerenes prefer the honeycomb lattice. Generally, Dirac bands appear in the honeycomb lattices consisting of C_n molecules when the systems considered possess C_3v symmetry. In the doped systems, the bandgap opens due to two mechanisms: the spin-orbit coupling from the heavy elements and the broken mirror symmetry due to the relative rotation between the C_n molecules. In particular, the former mechanism may induce a topologically nontrivial phase to realize the quantum spin Hall effect.