Exact ground states for the Hubbard model on the Kagome lattice

Abstract

The author gives a complete and rigorous description of the ground states of the Hubbard model on the Kagome lattice for electron densities n>or=5/3 and U>0. If 11/6>n>or=5/3 the system shows a ferromagnetic behaviour at zero temperature. If n is above 11/6 the system is paramagnetic. The proof of these results uses some graph-theoretic methods. The results are applicable to all line graphs of planar lattices, of which the Kagome lattice is an example.