Zhang GM, Shen SQ. Ordered valence-bond states in symmetric two-dimensional spin-orbital systems.
PHYSICAL REVIEW LETTERS 2001;
87:157201. [PMID:
11580721 DOI:
10.1103/physrevlett.87.157201]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2001] [Indexed: 05/23/2023]
Abstract
We consider a superexchange Hamiltonian, H = -SUM (<i,j>)(2S(i) . S(j)-(1/2)) (2T(i) . T(j)-(1/2)), 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 exactly, and a mean field theory has been developed. 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. An important relation has been found, relating the spin and orbital correlation functions to the combined spin-orbital ones.
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