Mott metal-insulator transition in the half-filled Hubbard model on the triangular lattice - art. no. 085104

We investigate the metal-insulator transition in the half-filled Hubbard mo del on the two-dimensional triangular lattice using both the Kotliar-Rucken stein slave-boson technique and an exact numerical diagonalization of finit e clusters. Contrary to the case of a square lattice, where a perfect nesti ng of the Fermi surface leads to a metal-insulator transition at arbitraril y small values of U, always accompanied by antiferromagnetic ordering, on a triangular lattice, due to the lack of perfect nesting, the transition tak es place at a finite value of U, and frustration induces a nontrivial compe tition among different magnetic phases. Indeed, within the mean-field appro ximation in the slave-boson approach, as the interaction grows the paramagn etic metal turns into a metallic phase with incommensurate spiral ordering. Increasing the interaction further, a linear spin density wave is stabiliz ed, and finally for strong coupling the latter phase undergoes a first-orde r transition toward an antiferromagnetic insulator. No trace of the interme diate phases is seen in the exact diagonalization results, indicating a tra nsition between a paramagnetic metal and an antiferromagnetic insulator.