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Ordered valence bond states in symmetric two-dimensional spin-orbital systems

Guang-Ming Zhang·Shun-Qing Shen
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Abstract

We consider a superexchange Hamiltonian, $H=-\sum_{ }(2{\bf S}_i\cdot {\bf S}_j-\frac 12)(2{\bf T}_i\cdot {\bf T}_j-\frac 12)$, which describes systems with orbital degeneracy and strong electron-phonon coupling in the limit of large on-site repulsion. In an SU(4) Schwinger boson representation, a reduced spin-orbital interaction is derived {\it exactly}, and a mean field theory has been developed by introducing a symmetric valence bond pairing order parameter. In one dimension, a spin-orbital liquid state with a finite gap is obtained. On a two-dimensional square lattice a novel type of spin-orbital ferromagnetically ordered state appears, while spin and orbital are antiferromagnetic. Moreover, an important relation has been found, relating the spin and orbital correlation functions to the combined spin-orbital ones.

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Guang-Ming Zhang, Shun-Qing Shen. 2001-08-08. Ordered valence bond states in symmetric two-dimensional spin-orbital systems. https://doi.org/10.1103/physrevlett.87.157201

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