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For topologically nontrivial and very narrow bands, Coulomb repulsion between electrons has been predicted to give rise to a spontaneous fractional quantum-Hall (FQH) state in absence of magnetic fields. We show that orbital degrees of freedom in frustrated lattice systems leads to a narrowing of topologically nontrivial bands for robust parameter ranges. We find that a strongly correlated t system on a triangular lattice can support a spin-chiral magnetic ordering pattern with such topologically nontrivial and flat bands. In order to go beyond mean field and to study the impact of longer-range
interactions, we map the low-energy electronic states onto an effective one-band model. Exact diagonalization is then used to establish signatures of a spontaneous FQH state.
[1] J. W. F. Venderbos, M. Daghofer and J. van den Brink, Phys. Rev. Lett. 107, 116401 (2011); J. W. F. Venderbos, S. Kourtis, J. van den Brink and M. Daghofer, arXiv:1109.5955 (2011). |
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