Stability of Ferromagnetism in Hubbard models on two-dimensional line graphs

TL;DR

This paper demonstrates that ferromagnetism in Hubbard models on two-dimensional line graphs remains stable under certain kinetic energy modifications, making it a promising model for metallic ferromagnetism.

Contribution

It introduces a modified Hubbard model on line graphs of planar bipartite graphs with stable ferromagnetic ground states under specific kinetic energy contributions.

Findings

Ferromagnetic ground state stability under added kinetic energy.

Model exhibits extended eigenstates with no degeneracy or band gap.

Suitable as a candidate for metallic ferromagnetism.

Abstract

It is well known that the Hubbard model on a line graph has a flat band and ferromagnetic ground states in a certain density range. We show that for a Hubbard model on a line graph of a planar bipartite graph the ferromagnetic ground state is stable if one adds a special contribution to the kinetic energy which lifts the degeneracy of the lowest single particle state. Stability holds for sufficiently strong repulsion U. The model has extended single particle eigenstates, no degeneracy, and no band gap. It is therefore a good candidate for metallic ferromagnetism.