Phys. Rev. B 45, 304–307 (1992)Hidden Z2×Z2 symmetry breaking in Haldane-gap antiferromagnetsReceived 29 July 1991; published in the issue dated 1 January 1992 We show that the Haldane phase of the S=1 antiferromagnetic chain is closely related to the breaking of a hidden Z2×Z2 symmetry. When the chain is in the Haldane phase, this Z2×Z2 symmetry is fully broken, but when the chain is in a massive phase other than the Haldane phase, e.g., the Ising phase or the dimerized phase, this symmetry is broken only partially or not at all. The hidden Z2×Z2 symmetry is revealed by introducing a nonlocal unitary transformation of the chain. This unitary transformation also leads to a simple variational calculation which qualitatively reproduces the phase diagram of the S=1 chain. © 1992 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevB.45.304
DOI:
10.1103/PhysRevB.45.304
PACS:
75.10.Jm, 75.30.Ds, 75.50.Ee
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