Robust Mottness and tunable interlayer magnetism in Nb3X8 (X = F, Cl, Br, I) bilayers

Breathing kagome materials Nb3X8 (X = F, Cl, Br, I) have attracted broad interest owing to their Mott insulating behavior and stacking-dependent magnetic ground states. However, the role of interlayer coupling in modulating these properties remains underexplored. Here, using density functional theory with Hubbard U corrections, we systematically investigated how interlayer coupling affects the Mott insulating states and magnetic ground states across 24 bilayer stacking configurations for each compound. We found that all bilayers remain Mott insulators, demonstrating robust Mottness. Driven by the competition between interlayer Pauli repulsion and hopping, most stackings favor interlayer AFM order, including conventional and compensated AFM, while some exhibit AFM-FM degeneracy or stabilize interlayer FM. This robustness of Mott states coexisting with tunable interlayer magnetism provides novel analysis and insights for research on breathing kagome Mott insulators.