We investigate internal localized eigenmodes of the linearized equation around spin discrete breathers in one-dimensional antiferromagnets with on-site easy-axis anisotropy. The threshold of occurrence of the internal localized eigenmodes has a typical structure in the parameter space depending on the frequency of the spin discrete breather. We also performed molecular-dynamics simulation in order to show the validity of our linear analysis.

• Received 11 December 2001

DOI:https://doi.org/10.1103/PhysRevB.66.212408