Abstract
Spontaneous charge ordering occurring in correlated systems may be considered as a possible route to generate effective lattice structures with unconventional couplings. For this purpose we investigate the phase diagram of doped extended Hubbard models on two lattices: (i) the honeycomb lattice with on-site and nearest-neighbor Coulomb interactions at filling and (ii) the triangular lattice with on-site , nearest-neighbor , and next-nearest-neighbor Coulomb interactions at filling (). We consider various approaches including mean-field approximations, perturbation theory, and variational Monte Carlo. For the honeycomb case (i), charge order induces an effective triangular lattice at large values of and , where is the nearest-neighbor hopping integral. The nearest-neighbor spin exchange interactions on this effective triangular lattice are antiferromagnetic in most of the phase diagram, while they become ferromagnetic when is much larger than . At , ferromagnetic and antiferromagnetic exchange interactions nearly cancel out, leading to a system with four-spin ring-exchange interactions. On the other hand, for the triangular case (ii) at large and finite , we find no charge order for small , an effective kagome lattice for intermediate , and one-dimensional charge order for large . These results indicate that Coulomb interactions induce [case (i)] or enhance [case(ii)] emergent geometrical frustration of the spin degrees of freedom in the system, by forming charge order.
19 More- Received 21 June 2016
- Revised 18 October 2016
DOI:https://doi.org/10.1103/PhysRevB.94.195111
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