Hubbard models with nearly flat bands: Ground-state ferromagnetism driven by kinetic energy

  title={Hubbard models with nearly flat bands: Ground-state ferromagnetism driven by kinetic energy},
  author={Patrick E. Muller and Johannes Richter and Oleg Derzhko},
  journal={Physical Review B},
We consider the standard repulsive Hubbard model with a flat lowest-energy band for two one-dimensional lattices (diamond chain and ladder) as well as for a two-dimensional lattice (bilayer) at half filling of the flat band. The considered models do not fall in the class of Mielke-Tasaki flat-band ferromagnets, since they do not obey the connectivity conditions. However, the ground-state ferromagnetism can emerge, if the flat band becomes dispersive. To study this kinetic-energy-driven… 
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