Intrinsic self-localized magnons in one-dimensional antiferromagnets

The nonlinearity in magnon systems in one-dimensional Heisenberg antiferromagnets is shown to produce two types of intrinsic self-localized modes, symmetric and antisymmetric, below the magnon frequency band. In the case of extreme localization, the localized modes can be viewed as a two-spin bound state or a local spin-liquid state, where a pair of spins undergoes a large excursion as compared with the rest of the spins.