Magnon decay in gapped quantum spin systems

TL;DR

This paper investigates magnon decay processes in gapped quantum spin systems, revealing conditions under which two-magnon decay occurs and comparing theoretical predictions with experimental data.

Contribution

It demonstrates that symmetry considerations permit two-magnon decay in certain gapped spin systems, extending previous sigma-model predictions.

Findings

Two-magnon decay occurs in Haldane gap S=1 chains.

Decay rates are computed for specific model systems.

Comparison with experimental data supports the theoretical predictions.

Abstract

In the O(3) sigma-model description of gapped spin systems, S=1 magnons can only decay into three lower energy magnons. We argue that the symmetry of the quantum spin Hamiltonian often allows decay into two magnons, and compute this decay rate in model systems. Two magnon decay is present in Haldane gap S=1 spin chains, even though it cannot be induced by any allowed term written in powers and gradients of the sigma-model field. We compare our results with recent measurements of Stone et al. (cond-mat/0511266) on a two-dimensional spin system.