Ordering Phenomena in Transition Metal Oxides

Finite-Temperature Mott Transitions in 2D Frustrated Electron Systems   

We investigate the Hubbard model on two typical frustrated lattices in two dimensions, the Kagome lattice and the anisotropic triangular lattice, by means of the cellular dynamical mean field theory. We show that the metallic phase is stabilized up to fairly large Hubbard interactions under strong geometrical frustration in both cases, which gives rise to heavy fermion behavior and several anomalous properties around the Mott transition point. In particular, for the anisotropic triangular lattice, we find novel reentrant behavior in the Mott transition in the moderately frustrated parameter regime, which is caused by the competition between Fermi-liquid formation and magnetic correlations. It is demonstrated that the reentrant behavior is a generic feature inherent in the Mott transitions with intermediate geometrical frustration, and indeed consistent with recent experimental findings for some organic materials.