The Heisenberg antiferromagnet chain realizes the Haldane phase: a gapped symmetry-protected topological phase with effective spin one-half degrees of freedom at open ends. Time-reversal symmetry is one possible protecting symmetry. Integer spin alone does not imply the same protected class: odd- and even-integer chains differ. The broader gap distinction is the Haldane conjecture.[ref]
Nobel Lecture: Topological quantum matter by F. Duncan M. Haldane. Haldane, individual Nobel lecture, p. 040502-9, Fig. 8 and odd-integer versus even-integer distinction
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