Fig. 4: Flat-band induced enhancement of the AFM spin fluctuations in kagome Hubbard model.

a Band structure of the ideal kagome model. The green, blue, and red dash-dot lines correspond to the Fermi level at filling levels of n  =  3.6, 3.7, and 3.8, respectively. b–g Leading eigenvalues of spin susceptibilities for the kagome Hubbard model under different filling levels, calculated at U  =  2t. b–d are calculated with all three bands, e–g are calculated without the flat band. h Leading eigenvalues of the bare electron susceptibility at filling level of n = 3.8. The black arrows point to the ring-shaped peak sets originating from the Fermi surface nesting, which do not vary upon excluding the flat band, while the AFM peaks around the K points are intimately related to the flat band.