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Orbital degrees of freedom in frustrated lattice systems can lead to qualitatively and quantitively new effects. It will be shown that in particular cases it can cause a narrowing of topologically nontrivial bands. This robust effect does not rely on fine-tuned long-range hopping parameters and is directly relevant to a wide class of transition-metal compounds. As a consequence in such systems a fractional quantum Hall effect is predicted to occur in the absence of magnetic fields and at high temperature in these lattice systems that have flat bands with a nonzero Chern number [1]. In particular correlated electrons in a t2g-orbital system on a triangular lattice self-organize into a spin-chiral magnetic ordering pattern that induces precisely the required topologically nontrivial and flat bands [2].
[1] J. Venderbos, M. Daghofer and JvdB, Phys. Rev. Lett. 107, 116401 (2011). [2] J. Venderbos, S. Kourtis, JvdB and M. Daghofer, Preprint ArXiv:1109.5955 (2011). |
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