paper

Semiclassical description of spin ladders

arXiv:cond-mat/9506026 · doi:10.1103/PhysRevB.52.15319

Abstract

The Heisenberg spin ladder is studied in the semiclassical limit, via a mapping to the nonlinear model. Different treatments are needed if the inter-chain coupling is small, intermediate or large. For intermediate coupling a single nonlinear model is used for the ladder. Its predicts a spin gap for all nonzero values of if the sum of the spins of the two chains is an integer, and no gap otherwise. For small , a better treatment proceeds by coupling two nonlinear sigma models, one for each chain. For integer , the saddle-point approximation predicts a sharp drop in the gap as increases from zero. A Monte-Carlo simulation of a spin 1 ladder is presented which supports the analytical results.

8 pages, RevTeX 3.0, 4 PostScript figures

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