Flat band ferromagnetism without connectivity conditions in the flat band
Department of Theoretical Physics, University of Debrecen - H-4010 Debrecen, Hungary
Received: 24 June 2014
Accepted: 14 August 2014
It is known that a system which exhibits a half-filled lowest flat band and the localized one-particle Wannier states on the flat band satisfying the connectivity conditions, is always ferromagnetic. Without the connectivity conditions on the flat band, the system is non-magnetic. We show that this is not always true. The reason is connected to a peculiar behavior of the band situated just above the flat band.
PACS: 71.10.Fd – Lattice fermion models (Hubbard model, etc.) / 71.27.+a – Strongly correlated electron systems; heavy fermions / 03.65.Aa – Quantum systems with finite Hilbert space
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