Metal insulator transition to a partial disordered state in the 1/3 filled Hubbard model on a triangular lattice

The interplay of electron filling, electron-electron interactions, and geometric frustration
facilitates the emergence of novel electronic phases in both material and model systems.
In the Hubbard on the triangular lattice, one can study of the effect of all three components
on the formation of collective states of charge and magnetic degrees of freedom. We
present results from a mean-field study of the 1/3 filled Hubbard model on the triangular
lattice. With on-site interactions (U) only, we observe a two step process in the ground state
where a paramagnetic metal develops noncollinear magnetic correlations at a finite interaction
strength, U^*/t ≈ 4.70, followed by a metal insulator transition (MIT) to a charge ordered and
partial ordered magnetic state at U_c/t ≈ 5.10. In the insulating phase, excess charge density
and collinear antiferromagnetic order define a honeycomb substructure of the parent triangular
lattice. The remaining sites defining a triangular substructure contain reduced charge density
and are paramagnetic. For U/t > U_c/t, the MIT occurs at T_c/t ≈ 0.16 and is weakly first order.
The effects of filling, frustration, and nearest neighbor Coulomb repulsion V on the MIT
are discussed briefly.