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arXiv:cond-mat/0604076 · Physical Review B

Spin-orbital gap of multiorbital antiferromagnet with geometrical frustration

Hiroaki Onishi, Takashi Hotta

Published Jan 10, 2007• 0 citations
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Abstract

In order to discuss the spin-gap formation in a multiorbital system, we analyze an ${e}_{g}$-orbital Hubbard model on a geometrically frustrated zigzag chain by using a density-matrix renormalization group method. Due to the appearance of a ferro-orbital arrangement, the system is regarded as a one-orbital system, while the degree of spin frustration is controlled by the spatial anisotropy of the orbital. In the region of strong spin frustration, we observe a finite energy gap between ground and first-excited states, which should be called a spin-orbital gap. The physical meaning is clarified by an effective Heisenberg spin model including the correct effect of the orbital arrangement influenced by the spin excitation.

DOI
10.1103/physrevb.75.014410

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In order to clarify a key role of the orbital degree of freedom in the spin S=1S=1S=1 Haldane system, we investigate ground-state properties of the t2g{t}_{2g}t2g​-orbital degenerate Hubbard model on the linear chain by using numerical techniques. Increasing the Hund's rule coupling in multiorbital systems, in general, there occurs a transition from an antiferromagnetic to a ferromagnetic phase. We find that the antiferromagnetic phase is described as the Haldane system with spin gap, while in the ferromagnetic phase, there exists the gapless excitation with respect to the orbital degree of freedom. Possible relevance of the present results to actual systems is also discussed.
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