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Andreas Mielke: Ferromagnetism in the Hubbard model on line graphs and further considerations
J. Phys. A: Math. Gen.24,
AbstractLet L(G) be the line graph of a graph G=(V,E). The Hubbard model on L(G) has ferromagnetic ground states with a saturated spin if the interaction is repulsive (U>0) and if the number of electrons N satisfies N>or=M. M= mod E mod + mod V mod -1 if G is bipartite and M= mod E mod + mod V mod otherwise. The author shows that the ferromagnetic ground state is unique if N=M. Further he gives a sufficient condition for the existence of other ground states if N>M. The results are valid also for a multi-band Hubbard model on a bipartite graph. In the case of a periodic lattice, the results are related to the existence of a flat energy band.
title="Ferromagnetism in the Hubbard model on line graphs and further considerations",
journal="J. Phys. A: Math. Gen.",
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