Abstract
Nagaoka's theorem on ferromagnetism in the Hubbard model with one electron fewer than half filling is generalized to the case where all possible nearest-neighbor Coulomb interactions (the density-density interaction , bond-charge interaction , exchange interaction , and hopping of double occupancies ) are included. It is shown that for ferromagnetic exchange coupling () ground states with maximum spin are stable already at finite Hubbard interaction . For nonbipartite lattices this requires a hopping amplitude . For vanishing one obtains as in Nagaoka's theorem. This shows that the exchange interaction is important for stabilizing ferromagnetism at finite . Only in the special case is the ferromagnetic state stable even for , provided the lattice allows the hole to move around loops.
- Received 3 November 1995
DOI:https://doi.org/10.1103/PhysRevB.53.9225
©1996 American Physical Society