Local susceptibilities in semi-infinite antiferromagnetic chains: Elementary perspectives

Abstract
Using conformal field theory methods Eggert and Affleck [Phys. Rev. Lett. 75, 984 (1996)] have shown that the semi-infinite S=1/2 Heisenberg antiferromagnetic chain exhibits a remarkable alternation in its local response to a uniform field at low temperatures. Such alternation is not an essentially quantum effect: A similar, and sometimes stronger, susceptibility alternation is a feature of classical Heisenberg-Ising chains at T=0. In S=1/2 chains, susceptibility alternation is not unique to the Heisenberg model, but can be seen in expansions about the Ising model and also in the XY model.
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