Partial order in the extended Hubbard model on a triangular lattice

The list of new materials which possess charge, spin, and orbital degrees
of freedom all competing within a geometrically frustrated environment
continues to grow. Such systems are intriguing because they are apt to
exhibit new collective phases of matter. Theoretical work in this area has
increased too, but theoretical and numerical studies of frustrated models
of interacting fermions are difficult for a host of reasons. The application
of mean-field theory is typically a good starting point for the study of
the phase diagram of a strongly correlated many-body model. Hence,
focusing on charge and magnetic degrees of freedom of fermions, we present
results from Hartree-Fock calculations of the extended Hubbard model on
the triangular lattice. We emphasize the case of 1/3 filling where
a finite temperature metal-insulator transition can be induced for select
values of the on-site (U) and nearest-neighbor (V) Coulomb repulsions,
including a phase with partial order confined to the honeycomb substructure
of the parent triangular lattice.