We uncover four coupled spin-charge ground states in the strong coupling limit of the Kondo lattice model at various electronic fillings on a frustrated decorated honeycomb lattice, where each regular honeycomb sublattice point is occupied by three-site triangular units. We employ a hybrid Markov Chain Monte Carlo (hMCMC) simulation method which combines classical MCMC for localized spins and exact diagonalization of the electronic Hamiltonian. Two of the spin-charge ground states, respectively, consists of three-site and six-site ferromagnetic (FM) clusters arranged in antiFM and ${120}^{\circ }$ Yafet-Kittel (YK) phase which we label as S-AF (super-antiferromagnet) and S-YK (super-YK), respectively. Two even more interesting coupled spin-charge states, respectively accommodate FM dimers and trimers (as three-site line segment), which we label as FM-D and FM-T. In both cases, the antiFM aligned dimers and trimers in respective phases, are arranged in stripes along one of three lattice directions: the spontaneously symmetry broken phases giving rise to nontrivial macroscopic degeneracy. These underlying magnetic textures (except S-YK state) restrict electrons in fragmented small regions (e.g., triangular units, two-site dimers, three-site line segments, respectively, in S-AF, FM-D and FM-T), resulting in flat bands by opening large gaps in electronic density of states, which in turn stabilize these coupled spin-charge states: a “band effect”. These exotic spin-charge ground states could be relevant to electron-doped spin systems resulting from various metal-organic frameworks, which have attracted significant attention to condensed matter physics.

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• Flat bands
• Magnetic phase transitions
• Magnetic texture
• Magnetism
• Antiferromagnets
• Monte Carlo methods