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 ground state. 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 .
- Received 16 October 1996
DOI:https://doi.org/10.1103/PhysRevLett.78.1984
©1997 American Physical Society