Ferromagnetism in the Hubbard model with Topological/Non-Topological Flat Bands

Understand

We introduce and study two classes of Hubbard models with magnetic flux or with spin-orbit coupling, which have a flat lowest band separated from other bands by a nonzero gap.

• We study the Chern number of the flat bands, and find that it is zero for the first class but can be nontrivial in the second.
• We also prove that the introduction of on-site Coulomb repulsion leads to ferromagnetism in both the classes.