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We consider the antiferromagnetic Heisenberg and the repulsive Hubbard model on two one-dimensional lattices,
which support dispersionless (flat) one-particle states corresponding to localized states on triangular trapping cells.
The flat band is two-fold degenerate that is related to the chirality degrees of freedom associated to the triangle.
We calculate the degeneracy of the localized states as well as the contribution of these states to thermodynamic quantities.
We also discuss the effect of extra interactions, which lift the degeneracy present due to the chirality of the localized states on triangles.
The flat-band states set an extra low-energy scale in the system
and lead to well-pronounced features in the low-temperature thermodynamic
quantities at high magnetic fields or low electron densities.
Further details can be found in: M. Maksymenko, O. Derzhko, J. Richter, Eur. Phys. J. B 84, 397 (2011). |
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