Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2008-06-05
Int. J. Modern Phys. B 22, 4418 (2008)
Physics
Condensed Matter
Strongly Correlated Electrons
16 pages, 6 figure, the paper is based on an invited talk on the XXXI International Workshop on Condensed Matter Theories, Ban
Scientific paper
10.1142/S0217979208050176
We report on recent studies of the spin-half Heisenberg and the Hubbard model on the sawtooth chain. For both models we construct a class of exact eigenstates which are localized due to the frustrating geometry of the lattice for a certain relation of the exchange (hopping) integrals. Although these eigenstates differ in details for the two models because of the different statistics, they share some characteristic features. The localized eigenstates are highly degenerate and become ground states in high magnetic fields (Heisenberg model) or at certain electron fillings (Hubbard model), respectively. They may dominate the low-temperature thermodynamics and lead to an extra low-temperature maximum in the specific heat. The ground-state degeneracy can be calculated exactly by a mapping of the manifold of localized ground states onto a classical hard-dimer problem, and explicit expressions for thermodynamic quantities can be derived which are valid at low temperatures near the saturation field for the Heisenberg model or around a certain value of the chemical potential for the Hubbard model, respectively.
Derzhko Oleg
Honecker Andreas
Richter Jadwiga
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