Exotic coupled spin-charge states in decorated honeycomb magnets: A hybrid-Monte Carlo study

Abstract

We uncover four exotic 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 anti-FM 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 anti-FM 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 non-trivial 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 (MOFs), which have attracted significant attention to condensed matter physics