Theory of High-Temperature Fractional Chern Phases in Monolayer van der Waals Kagome Materials A 2 T 3 X 4

Fractional Chern insulators bring the fractional quantum Hall effect, with its anyonic excitations, to zero magnetic field. So far they have been realized in moiré materials, where the long superlattice period weakens electronic interactions and confines these phases to cryogenic temperatures. Early proposals instead envisioned topological flat bands on atomic-scale lattices, where fractionalization could persist to far higher temperatures, but a suitable material has been lacking. Here we theoretically identify monolayers of the recently synthesized van der Waals kagome family A 2 T 3 X 4 as such a platform, combining intrinsic topological flat bands and strong Coulomb interactions with gate-tunable carrier density and layer assembly. Exact diagonalization of models derived from density functional theory reveals ferromagnetism over broad filling ranges, supporting diverse fractional Chern insulators, anomalous composite Fermi liquids, and charge-ordered phases. In particular, in Cs 2 Pd 3 S 4, the fractional Chern insulator exhibits a many-body gap of approximately 26 meV in the largest system accessible with band mixing allowing at most one interband electron-hole excitation. Layer assembly further provides a natural route to fractional quantum spin Hall insulators: bilayers with antiparallel magnetizations support this phase at realistic separations. These results identify an experimentally accessible material family in which chemical composition, carrier density, and stacking offer complementary routes to fractionalization at enhanced energy scales and control over topological order.