paper

Magnetization plateaus in spin chains: ``Haldane gap'' for half-integer spins

arXiv:cond-mat/9610168 · doi:10.1103/PhysRevLett.78.1984

Abstract

We discuss zero-temperature quantum spin chains in a uniform magnetic field, with axial symmetry. For integer or half-integer spin, , the magnetization curve can have plateaus and we argue that the magnetization per site is topologically quantized as at the plateaus, where is the period of the groundstate. We also discuss conditions for the presence of the plateau at those quantized values. For and , we study several models and find two distinct types of massive phases at the plateau. One of them is argued to be a ``Haldane gap phase'' for half-integer .

Revised version, to appear in Phys. Rev. Lett. (no changes in main conclusions); 5 pages, REVTEX with 2 figures in eps

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